2D and 3D shapes can exhibit different colors. And just like the other transformations, adding color to a shape produces a new shape, one with color.

color([r,g,b], object, object2 ...); // for example, color([1,1,0],sphere());
color([r,g,b], array);
color([r,g,b,a], object, object2 ...);
color([r,g,b,a], array);
color(name, object, object2 ...); // for example, color('red',sphere());
color(name, a, object, object2 ...); // for example, color('red',0.5, sphere());
color(name, array);
color(name, a, array);

Whereas the named colors are case-insensitive, e.g. 'RED' is the same as 'red'.

using CSG objects' built in methods (r, g, b must be between 0 and 1, not 0 and 255):

object.setColor([r,g,b]);
object.setColor([r,g,b,a]);
object.setColor(r,g,b);
object.setColor(r,g,b,a);
object.setColor(css2rgb('dodgerblue'));

Examples:

color([1,0.5,0.3],sphere(1));                      // openscad like
color([1,0.5,0.3],sphere(1),cube(2));
color("Red",sphere(),cube().translate([2,0,0]));   // named color (case-insensitive)
 
sphere().setColor(1,0.5,0.3);                      // built in methods
sphere().setColor([1,0.5,0.3]);   

See the [https://www.w3.org/TR/css3-color/#svg-color Extended Color Keywords] for all available colors.

Code excerpt:

o.push( color([1,0,0],sphere()) );
o.push( color([0,1,0],cube()) );
o.push( color([0,0,1],cylinder()) );
 
o.push( color("red",sphere()) );
o.push( color("green", cube()) );
o.push( color("blue", cylinder()) );
 
for(var i=0; i<1; i+=1/12) {
   o.push( cube().setColor(hsl2rgb(i,1,0.5)) );
}

Code:

function main() {
   var o = [];
   for(var i=0; i<8; i++) {
      o.push(cylinder({r:3,h:20}).
         setColor(
            hsl2rgb(i/8,1,0.5).  // hsl to rgb, creating rainbow [r,g,b]
            concat(1/8+i/8)      // and add to alpha to make it [r,g,b,a]
         ).translate([(i-3)*7.5,0,0])
      );
   }
   o.push(color("red",cube(5)).translate([-4,-10,0]));
   o.push(color("red",0.5,cube(5)).translate([4,-10,0]));
   return o;
}

Note: There are some Transparency_Sorting|OpenGL Transparency Limitations, e.g. and depending on the order of colors, you might not see through otherwise partially transparent objects.

Following functions to convert between color spaces.

var hsl = rgb2hsl(r,g,b); // or rgb2hsl([r,g,b]);
var rgb = hsl2rgb(h,s,l); // or hsl2rgb([h,s,l]);
var hsv = rgb2hsv(r,g,b); // or rgb2hsv([r,g,b]);
var rgb = hsv2rgb(h,s,v); // or hsv2rgb([h,s,v]);

whereas

• r,g,b (red, green, blue)
• h,s,l (hue, saturation, lightness)
• h,s,v (hue, saturation, value)

E.g. to create a rainbow, t = 0..1 and .setColor(hsl2rgb(t,1,0.5))

See the http://openjscad.org/#examples/slices/tor.jscad Tor (multi-color) for an example.