color bullseyes by ring count in qqlrs

art.rs.patch

diff --git a/src/art.rs b/src/art.rs
index 953bf99..ffec2d1 100644
--- a/src/art.rs
+++ b/src/art.rs
@@ -1431,14 +1431,21 @@ fn draw_ring_dot(pt: &Point, pctx: &mut PaintCtx, rng: &mut Rng) {
         variance_adjust * rescale(num_rings as f64, (1.0, 7.0), (0.022, 0.008))
     };
 
+    // https://personal.sron.nl/~pault/
+    const SEQ: [Rgb; 7] = [
+        Rgb(68.0, 119.0, 170.0),
+        Rgb(102.0, 204.0, 238.0),
+        Rgb(34.0, 136.0, 51.0),
+        Rgb(204.0, 187.0, 68.0),
+        Rgb(238.0, 102.0, 119.0),
+        Rgb(170.0, 51.0, 119.0),
+        Rgb(187.0, 187.0, 187.0),
+    ];
+
     let mut band_num = 0;
     let mut r = pt.scale;
     while r > w(0.0004) {
-        let color = if band_num % 2 == 0 {
-            pt.primary_color
-        } else {
-            pt.secondary_color
-        };
+        let source = SEQ[num_rings as usize - 1].to_source();
         band_num += 1;
 
         let band_center_x = rng.gauss(pt.position.0, w(0.0005).min(r * position_variance));
@@ -1463,7 +1470,7 @@ fn draw_ring_dot(pt: &Point, pctx: &mut PaintCtx, rng: &mut Rng) {
             r,
             final_thickness,
             variance_adjust,
-            color,
+            source,
             pctx,
             rng,
         );
@@ -1477,12 +1484,10 @@ fn draw_messy_circle(
     r: f64,
     thickness: f64,
     variance_adjust: f64,
-    color: Hsb,
+    source: Source,
     pctx: &mut PaintCtx,
     rng: &mut Rng,
 ) {
-    let source = color.to_rgb().to_source();
-
     let num_rounds_divisor = if thickness > w(0.02) {
         rescale(thickness, (w(0.02), w(0.04)), (w(0.00021), w(0.00022)))
     } else if thickness > w(0.006) {