Painted rectangles
When the animation is off, you can click on the lower right corner of the rectangle, and move it to get a different rectangle.
Turn animation on and a simple sequence of rectangles will be drawn, each painted with rectangles.
You can change the maximum number of rectangles drawn.
To change colours, enter your choice of colours, separated by commas and a space.
You have to enter colours that javascript will understand, e.g., red, cyan, etc. Or anything javascript will understand, such as #110000, #550000, #990000, black
x and y values of lower right corner, given in pixels
The "alpha" should be between 0 and 1.
I recommend turning the animation off, and switching effect to "effect 1" to experiment with changing variables.

Max number of rectangles: Colours: rectangle x= y=
"global alpha" (opacity) speed canvas width= height= Presets:
Some of these presets are a bit random - that is, there are too many nice combinations, so these are not necessarily better than others! Let me know some settings you like, and I can add them too!

examples: Try 10 rectangles with just one colour
I put initial values of the colours as magenta, yellow, cyan, since all the other colours can be made from these. Try changing the order; try different colours. Try including white, or black

If you have a large number of rectangles allowed, then you might want to reduce the opacity and the speed

Random thoughs/digression

Move around the vertex; find interesting things. E.g., x=441, y=386.... looks like these must be close to ratio with small values... with these values, count looks like approx 8/7 squares in the picture. We have 441/7=63 but 386/8 = 48.25. 385/7=55.... have to work out what this means? change to 440/386 gives very different picture, if the number of rectangles is set to 1000; won't change so much for 10 rectangles.
Something about this relates to how very different numbers lie right next to each other.

Suppose there were an infinite number of colours allowed. Now set alpha to 1, so none are see through. How many rectangles (up to scaling) are there for which exactly n different colours can be seen? For example, for oue colour, we need a square. How many rectangles are three colours? These questions might not make sense - answers might be infinity... so how about colour a point (x,y) in colour i if there are i colours appearing in the rectangle of size (x,y) - what does the picture look like?
Lots of randomly interesting things to find. Eg. ratios I like: 366/220. tried with 10 rectangles; tried with 100, different; put to 1000, very similar to 10 rectangles. Why? Changed vertex corner a bit, until things lined up best: get 360/216 = 5/3. So 366/220 is close enough to 5/3 to get a similar look.