More than just this "color to alpha", this post describes in detail useful methods and approach to ImageMagick manipulation.
Lightbox JS is a simple, unobtrusive script used to overlay images on the current page. It's a snap to setup and works on all modern browsers.
This JavaScript VectorGraphics library provides graphics capabilities for JavaScript: functions to draw circles, ellipses (ovals), oblique lines, polylines and polygons (for instance triangles, rectangles) dynamically into a webpage. Usage of this Vector