The color plugin is only 4kb so much cheaper than the UI library. Of course you'll want to use a decent version of the plugin and not some buggy old thing which doesn't handle Safari and crashes when the transitions are too fast. Since a minified version isn't supplied you might like test various compressors and make your own min version. YUI gets the best compression in this case needing only 957 bytes and since it is so small - here it is:
(function(d){d.each(["backgroundColor","borderBottomColor","borderLeftColor","borderRightColor","borderTopColor","color","outlineColor"],function(f,e){d.fx.step[e]=function(g){if(!g.colorInit){g.start=c(g.elem,e);g.end=b(g.end);g.colorInit=true}g.elem.style[e]="rgb("+[Math.max(Math.min(parseInt((g.pos*(g.end[0]-g.start[0]))+g.start[0]),255),0),Math.max(Math.min(parseInt((g.pos*(g.end[1]-g.start[1]))+g.start[1]),255),0),Math.max(Math.min(parseInt((g.pos*(g.end[2]-g.start[2]))+g.start[2]),255),0)].join(",")+")"}});function b(f){var e;if(f&&f.constructor==Array&&f.length==3){return f}if(e=/rgb\(\s*([0-9]{1,3})\s*,\s*([0-9]{1,3})\s*,\s*([0-9]{1,3})\s*\)/.exec(f)){return[parseInt(e[1]),parseInt(e[2]),parseInt(e[3])]}if(e=/rgb\(\s*([0-9]+(?:\.[0-9]+)?)\%\s*,\s*([0-9]+(?:\.[0-9]+)?)\%\s*,\s*([0-9]+(?:\.[0-9]+)?)\%\s*\)/.exec(f)){return[parseFloat(e[1])*2.55,parseFloat(e[2])*2.55,parseFloat(e[3])*2.55]}if(e=/#([a-fA-F0-9]{2})([a-fA-F0-9]{2})([a-fA-F0-9]{2})/.exec(f)){return[parseInt(e[1],16),parseInt(e[2],16),parseInt(e[3],16)]}if(e=/#([a-fA-F0-9])([a-fA-F0-9])([a-fA-F0-9])/.exec(f)){return[parseInt(e[1]+e[1],16),parseInt(e[2]+e[2],16),parseInt(e[3]+e[3],16)]}if(e=/rgba\(0, 0, 0, 0\)/.exec(f)){return a.transparent}return a[d.trim(f).toLowerCase()]}function c(g,e){var f;do{f=d.curCSS(g,e);if(f!=""&&f!="transparent"||d.nodeName(g,"body")){break}e="backgroundColor"}while(g=g.parentNode);return b(f)}var a={aqua:[0,255,255],azure:[240,255,255],beige:[245,245,220],black:[0,0,0],blue:[0,0,255],brown:[165,42,42],cyan:[0,255,255],darkblue:[0,0,139],darkcyan:[0,139,139],darkgrey:[169,169,169],darkgreen:[0,100,0],darkkhaki:[189,183,107],darkmagenta:[139,0,139],darkolivegreen:[85,107,47],darkorange:[255,140,0],darkorchid:[153,50,204],darkred:[139,0,0],darksalmon:[233,150,122],darkviolet:[148,0,211],fuchsia:[255,0,255],gold:[255,215,0],green:[0,128,0],indigo:[75,0,130],khaki:[240,230,140],lightblue:[173,216,230],lightcyan:[224,255,255],lightgreen:[144,238,144],lightgrey:[211,211,211],lightpink:[255,182,193],lightyellow:[255,255,224],lime:[0,255,0],magenta:[255,0,255],maroon:[128,0,0],navy:[0,0,128],olive:[128,128,0],orange:[255,165,0],pink:[255,192,203],purple:[128,0,128],violet:[128,0,128],red:[255,0,0],silver:[192,192,192],white:[255,255,255],yellow:[255,255,0],transparent:[255,255,255]}})(jQuery);