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+//////////////////////////////////////////////////////////////////////
+// LibFile: color.scad
+//   HSV and HSL conversion, and raindow module for coloring multiple objects.
+// Includes:
+//   include <BOSL2/std.scad>
+// FileGroup: Basic Modeling
+// FileSummary: HSV and HSL conversion, color multiple objects
+// FileFootnotes: STD=Included in std.scad
+//////////////////////////////////////////////////////////////////////
+
+
+// Section: Coloring Objects
+
+// Module: rainbow()
+// Usage:
+//   rainbow(list) ...
+// Description:
+//   Iterates the list, displaying children in different colors for each list item.
+//   This is useful for debugging lists of paths and such.
+// Arguments:
+//   list = The list of items to iterate through.
+//   stride = Consecutive colors stride around the color wheel divided into this many parts.
+//   maxhues = max number of hues to use (to prevent lots of indistinguishable hues)
+//   shuffle = if true then shuffle the hues in a random order.  Default: false
+//   seed = seed to use for shuffle
+// Side Effects:
+//   Sets the color to progressive values along the ROYGBIV spectrum for each item.
+//   Sets `$idx` to the index of the current item in `list` that we want to show.
+//   Sets `$item` to the current item in `list` that we want to show.
+// Example(2D):
+//   rainbow(["Foo","Bar","Baz"]) fwd($idx*10) text(text=$item,size=8,halign="center",valign="center");
+// Example(2D):
+//   rgn = [circle(d=45,$fn=3), circle(d=75,$fn=4), circle(d=50)];
+//   rainbow(rgn) stroke($item, closed=true);
+module rainbow(list, stride=1, maxhues, shuffle=false, seed)
+{
+    ll = len(list);
+    maxhues = first_defined([maxhues,ll]);
+    huestep = 360 / maxhues;
+    huelist = [for (i=[0:1:ll-1]) posmod(i*huestep+i*360/stride,360)];
+    hues = shuffle ? shuffle(huelist, seed=seed) : huelist;
+    for($idx=idx(list)) {
+        $item = list[$idx];
+        HSV(h=hues[$idx]) children();
+    }
+}
+
+
+// Section: Colorspace Conversion
+
+// Function&Module: HSL()
+// Usage:
+//   HSL(h,[s],[l],[a]) ...
+//   rgb = HSL(h,[s],[l]);
+// Description:
+//   When called as a function, returns the [R,G,B] color for the given hue `h`, saturation `s`, and lightness `l` from the HSL colorspace.
+//   When called as a module, sets the color to the given hue `h`, saturation `s`, and lightness `l` from the HSL colorspace.
+// Arguments:
+//   h = The hue, given as a value between 0 and 360.  0=red, 60=yellow, 120=green, 180=cyan, 240=blue, 300=magenta.
+//   s = The saturation, given as a value between 0 and 1.  0 = grayscale, 1 = vivid colors.  Default: 1
+//   l = The lightness, between 0 and 1.  0 = black, 0.5 = bright colors, 1 = white.  Default: 0.5
+//   a = When called as a module, specifies the alpha channel as a value between 0 and 1.  0 = fully transparent, 1=opaque.  Default: 1
+// Example:
+//   HSL(h=120,s=1,l=0.5) sphere(d=60);
+// Example:
+//   rgb = HSL(h=270,s=0.75,l=0.6);
+//   color(rgb) cube(60, center=true);
+function HSL(h,s=1,l=0.5) =
+    let(
+        h=posmod(h,360)
+    ) [
+        for (n=[0,8,4]) let(
+            k=(n+h/30)%12
+        ) l - s*min(l,1-l)*max(min(k-3,9-k,1),-1)
+    ];
+
+module HSL(h,s=1,l=0.5,a=1) color(HSL(h,s,l),a) children();
+
+
+// Function&Module: HSV()
+// Usage:
+//   HSV(h,[s],[v],[a]) ...
+//   rgb = HSV(h,[s],[v]);
+// Description:
+//   When called as a function, returns the [R,G,B] color for the given hue `h`, saturation `s`, and value `v` from the HSV colorspace.
+//   When called as a module, sets the color to the given hue `h`, saturation `s`, and value `v` from the HSV colorspace.
+// Arguments:
+//   h = The hue, given as a value between 0 and 360.  0=red, 60=yellow, 120=green, 180=cyan, 240=blue, 300=magenta.
+//   s = The saturation, given as a value between 0 and 1.  0 = grayscale, 1 = vivid colors.  Default: 1
+//   v = The value, between 0 and 1.  0 = darkest black, 1 = bright.  Default: 1
+//   a = When called as a module, specifies the alpha channel as a value between 0 and 1.  0 = fully transparent, 1=opaque.  Default: 1
+// Example:
+//   HSV(h=120,s=1,v=1) sphere(d=60);
+// Example:
+//   rgb = HSV(h=270,s=0.75,v=0.9);
+//   color(rgb) cube(60, center=true);
+function HSV(h,s=1,v=1) =
+    assert(s>=0 && s<=1)
+    assert(v>=0 && v<=1)
+    let(
+        h = posmod(h,360),
+        c = v * s,
+        hprime = h/60,
+        x = c * (1- abs(hprime % 2 - 1)),
+        rgbprime = hprime <=1 ? [c,x,0]
+                 : hprime <=2 ? [x,c,0]
+                 : hprime <=3 ? [0,c,x]
+                 : hprime <=4 ? [0,x,c]
+                 : hprime <=5 ? [x,0,c]
+                 : hprime <=6 ? [c,0,x]
+                 : [0,0,0],
+        m=v-c
+    )
+    rgbprime+[m,m,m];
+
+module HSV(h,s=1,v=1,a=1) color(HSV(h,s,v),a) children();
+
+