RGB triples for USGS lithology colours http://pubs.usgs.gov/of/2005/1314/

Colours.py

colours = {
 'Alkali-feldpar syenite': (244, 60, 108),
 'Alkali-feldspar granite': (255, 209, 220),
 'Alkali-feldspar rhyolite': (254, 220, 126),
 'Alkali-feldspar trachyte': (254, 183, 134),
 'Alkalic intrusive rock': (255, 111, 145),
 'Alkalic volcanic rock': (194, 65, 0),
 'Alkaline basalt': (169, 101, 55),
 'Alluvial fan': (255, 255, 183),
 'Alluvial terrace': (250, 238, 122),
 'Alluvium': (255, 255, 137),
 'Amphibole schist': (150, 150, 150),
 'Amphibolite': (123, 0, 156),
 'Andesite': (177, 72, 1),
 'Anorthosite': (255, 149, 174),
 'Aplite': (255, 193, 183),
 'Arenite': (166, 252, 170),
 'Argillite': (225, 240, 216),
 'Arkose': (105, 207, 156),
 'Ash-flow tuff': (255, 239, 217),
 'Augen gneiss': (136, 127, 80),
 'Basalt': (221, 179, 151),
 'Beach sand': (228, 216, 190),
 'Bentonite': (192, 208, 192),
 'Bimodal suite': (255, 193, 111),
 'Biogenic rock': (247, 243, 161),
 'Biotite gneiss': (200, 134, 254),
 'Black shale': (219, 254, 188),
 'Blueschist': (192, 192, 192),
 'Calc-silicate rock': (70, 0, 140),
 'Calc-silicate schist': (182, 182, 206),
 'Calcarenite': (154, 206, 254),
 'Carbonate rock': (86, 224, 252),
 'Cataclasite': (136, 127, 80),
 'Chemical sedimentary rock': (205, 222, 255),
 'Chert': (154, 191, 192),
 'Clastic rock': (217, 253, 211),
 'Clay or mud': (255, 219, 103),
 'Claystone': (213, 230, 204),
 'Coal': (130, 0, 65),
 'Coarse-grained mixed clastic rock': (165, 170, 173),
 'Colluvium': (225, 227, 195),
 'Conglomerate': (183, 217, 204),
 'Coral': (255, 204, 153),
 'Dacite': (254, 205, 172),
 'Debris flow': (211, 202, 159),
 'Delta': (255, 250, 200),
 'Diabase': (214, 0, 0),
 'Diorite': (255, 51, 23),
 'Dolostone': (107, 195, 255),
 'Dune sand': (224, 210, 180),
 'Dunite': (176, 0, 42),
 'Eclogite': (206, 157, 255),
 'Eolian material': (224, 197, 158),
 'Evaporite': (1, 156, 205),
 'Exhalite': (217, 194, 163),
 'Felsic gneiss': (224, 188, 254),
 'Felsic metavolcanic rock': (255, 141, 255),
 'Felsic volcanic rock': (244, 139, 0),
 'Fine-grained mixed clastic rock': (149, 255, 202),
 'Flaser gneiss': (100, 2, 11),
 'Flood plain': (255, 255, 213),
 'Gabbro': (233, 147, 190),
 'Gabbroid': (172, 0, 0),
 'Glacial drift': (191, 167, 67),
 'Glacial outwash sediment': (255, 223, 133),
 'Glacial-marine sediment': (254, 219, 46),
 'Glaciolacustrine sediment': (254, 226, 88),
 'Glassy volcanic rock': (255, 195, 228),
 'Gneiss': (236, 214, 254),
 'Granite': (249, 181, 187),
 'Granitic gneiss': (213, 164, 254),
 'Granitoid': (221, 41, 114),
 'Granodiorite': (233, 121, 166),
 'Granofels': (163, 55, 253),
 'Granulite': (106, 0, 106),
 'Gravel': (236, 180, 0),
 'Graywacke': (184, 234, 195),
 'Greenschist': (237, 237, 243),
 'Greenstone': (0, 128, 0),
 'Greisen': (164, 73, 255),
 'Hawaiite': (198, 128, 80),
 'Hornblendite': (163, 1, 9),
 'Hornfels': (234, 175, 255),
 'Ignimbrite': (255, 229, 195),
 'Intermediate metavolcanic rock': (255, 0, 0),
 'Intermediate volcanic rock': (235, 96, 1),
 'Intrusive carbonatite': (117, 1, 7),
 'Iron formation': (185, 149, 152),
 'Keratophyre': (254, 103, 0),
 'Kimberlite': (193, 1, 10),
 'Lahar': (220, 213, 180),
 'Lake or marine sediment': (244, 239, 228),
 'Lampophyre': (228, 88, 145),
 'Landslide': (201, 190, 137),
 'Latite': (254, 117, 24),
 'Lava flow': (255, 162, 39),
 'Levee': (255, 250, 233),
 'Limestone': (67, 175, 249),
 'Loess': (245, 225, 189),
 'Mafic gneiss': (204, 183, 255),
 'Mafic metavolcanic rock': (185, 59, 104),
 'Mafic volcanic rock': (147, 60, 1),
 'Marble': (0, 0, 255),
 'Mass wasting material': (207, 187, 143),
 'Medium-grained mixed clastic rock': (144, 165, 101),
 'Melange': (187, 192, 197),
 'Meta-argillite': (201, 255, 201),
 'Metabasalt': (135, 43, 76),
 'Metaconglomerate': (233, 255, 233),
 'Metaluminous granite': (255, 179, 197),
 'Metamorphic rock': (167, 167, 255),
 'Metarhyolite': (255, 167, 255),
 'Metasedimentary rock': (125, 255, 125),
 'Metavolcanic rock': (255, 87, 255),
 'Mica schist': (177, 177, 177),
 'Migmatite': (159, 0, 202),
 'Mixed carbonate/clastic rock': (56, 180, 177),
 'Mixed coal and clastic rock': (110, 73, 9),
 'Mixed volcanic/clastic rock': (96, 204, 191),
 'Monzodiorite': (255, 169, 157),
 'Monzogabbro': (227, 119, 173),
 'Monzonite': (255, 39, 90),
 'Moraine': (255, 238, 191),
 'Mud flat': (228, 208, 190),
 'Mudflow': (229, 219, 179),
 'Mudstone': (207, 239, 223),
 'Mylonite': (109, 80, 51),
 'Nepheline syenite': (255, 27, 81),
 'Norite': (255, 214, 209),
 'Novaculite': (192, 174, 182),
 'Obsidian': (255, 209, 234),
 'Oil shale': (187, 255, 221),
 'Olistostrome': (141, 190, 205),
 'Orthogneiss': (179, 149, 255),
 'Orthoquartzite': (203, 239, 206),
 'Paragneiss': (144, 99, 255),
 'Peat': (255, 207, 129),
 'Pegmatite': (255, 239, 243),
 'Pelitic schist': (202, 202, 220),
 'Peralkaline granite': (252, 82, 98),
 'Peraluminous granite': (248, 190, 174),
 'Peridotite': (206, 0, 49),
 'Phonolite': (95, 57, 31),
 'Phosphorite': (191, 227, 220),
 'Phyllite': (180, 207, 228),
 'Phyllonite': (172, 127, 80),
 'Playa': (241, 229, 223),
 'Plutonic rock': (252, 110, 124),
 'Porphyry': (255, 225, 232),
 'Pumice': (255, 229, 243),
 'Pyroclastic': (255, 224, 222),
 'Pyroxenite': (148, 0, 35),
 'Quartz diorite': (232, 28, 0),
 'Quartz gabbro': (237, 167, 202),
 'Quartz latite': (254, 135, 54),
 'Quartz monzodiorite': (255, 129, 159),
 'Quartz monzogabbro': (255, 111, 91),
 'Quartz monzonite': (255, 99, 136),
 'Quartz syenite': (251, 35, 56),
 'Quartz-feldspar schist': (162, 162, 192),
 'Quartzite': (159, 255, 159),
 'Residuum': (255, 227, 137),
 'Rhyodacite': (254, 198, 42),
 'Rhyolite': (254, 204, 104),
 'Sand': (255, 203, 35),
 'Sand sheet': (219, 204, 169),
 'Sandstone': (205, 255, 217),
 'Schist': (219, 219, 231),
 'Sedimentary breccia': (167, 186, 134),
 'Sedimentary rock': (146, 220, 183),
 'Serpentinite': (0, 92, 0),
 'Shale': (172, 228, 200),
 'Silt': (255, 211, 69),
 'Siltstone': (214, 254, 154),
 'Skarn': (129, 3, 255),
 'Slate': (230, 205, 255),
 'Spilite': (201, 85, 126),
 'Stratified glacial sediment': (255, 229, 157),
 'Sub/supra-glacial sediment': (254, 230, 112),
 'Subaluminous granite': (255, 111, 107),
 'Syenite': (244, 26, 135),
 'Talus': (188, 175, 108),
 'Tectonic breccia': (176, 167, 120),
 'Tectonic melange': (208, 203, 176),
 'Tectonite': (132, 97, 62),
 'Tephrite': (133, 79, 43),
 'Terrace': (255, 246, 217),
 'Tholeite': (211, 157, 121),
 'Till': (210, 194, 124),
 'Tonalite': (252, 182, 182),
 'Trachyandesite': (201, 82, 1),
 'Trachybasalt': (236, 213, 198),
 'Trachyte': (254, 160, 96),
 'Troctolite': (255, 191, 206),
 'Trondhjemite': (255, 167, 188),
 'Tuff': (249, 211, 211),
 'Ultramafic intrusive rock': (232, 0, 55),
 'Ultramafitite': (160, 53, 0),
 'Unconsolidated material': (253, 244, 63),
 'Vitrophyre': (255, 195, 248),
 'Volcanic ash': (224, 176, 158),
 'Volcanic breccia': (255, 213, 157),
 'Volcanic carbonatite': (110, 37, 0),
 'Volcanic rock': (255, 183, 222),
 'Wacke': (189, 219, 241),
 'Welded tuff': (255, 243, 201)
}