geom-webgl workaround for individual colored faces: Until face/vertex attributes are implemented in https://github.com/thi-ng/geom, colored meshes for WebGL apps can be achieved by building the attribute buffers (semi)manually...

coloredmesh.cljs

(ns coloredmesh
    (:require
     [thi.ng.geom.core :as g]
     [thi.ng.geom.core.vector :as v]
     [thi.ng.geom.core.matrix :as mat :refer [M44]]
     [thi.ng.geom.aabb :as a]
     [thi.ng.geom.core.utils :as gu]
     [thi.ng.geom.webgl.core :as gl]
     [thi.ng.geom.webgl.arrays :as arrays]
     [thi.ng.geom.webgl.animator :as anim]
     [thi.ng.geom.webgl.buffers :as buf]
     [thi.ng.geom.webgl.shaders :as shader]
     [thi.ng.geom.webgl.shaders.basic :as basic]))

  (defn colored-verts
    "Flattens given seq of faces into seq of vertices and associates color with each.
    Returns vector of [vertices colors]"
    [faces col]
    (let [verts (apply concat faces)]
      [verts (repeat (count verts) col)]))

  (defn flat-map
    [f coll] (flatten (map f coll)))

  (defn ^:export start!
      []
      (let [gl        (gl/gl-context "main") ;; ID of canvas
            view-rect (gl/get-viewport-rect gl)
            ;; create centered box and tessellate each side
            ;; results in a seq of pairs of triangles
            sides     (->> (a/aabb 1) (g/center) (g/faces) (map gu/tessellate-3))
            ;; associate colors with vertices, one color per side (here face pair)
            col-verts (map colored-verts sides [[1 0 0 1] [0 1 0 1] [0 0 1 1] [1 1 0 1] [1 0 1 1] [0 1 1 1]])
            verts     (flat-map first col-verts)
            cols      (flat-map second col-verts)
            ;; build model spec w/ attribute buffers and associated shader
            ;; usually one would use one of the geom lib's mesh types & converters,
            ;; but they currently don't support face/vertex attribs (yet)
            model     (-> {:attribs      {:position {:data (arrays/float32 verts) :size 3}
                                          :color    {:data (arrays/float32 cols)  :size 4}}
                           :uniforms     {:proj     (gl/perspective 45 view-rect 0.1 100.0)
                                          :view     (mat/look-at (v/vec3 0 0 2) (v/vec3) v/V3Y)}
                           :mode         gl/triangles
                           :num-vertices (/ (count verts) 3)
                           :shader       (->> (basic/make-color-shader-spec {:use-attrib true :3d true})
                                              (sh/make-shader-from-spec gl))}
                          (buf/make-attribute-buffers-in-spec gl gl/static-draw))]
        (anim/animate
         (fn [[t frame]]
           (gl/set-viewport gl view-rect)
           (gl/clear-color-buffer gl 1 1 1 1)
           (gl/enable gl gl/depth-test)
           (buf/draw-arrays
            gl (assoc-in model [:uniforms :model] (-> M44 (g/rotate-x t) (g/rotate-y (* t 2)))))
           true))))

(start!)