Actually you can further extend color. Color it self is on a 3 dimensional space (RGB). Now you have 6 dimensions to play with. Although in practice I found that doing Brightness and (Red/Blue) is a good way.<p>If you are doing points on a multi dimensional space, you can start using various shapes (Length, Width, Height) or Number of faces. Alternatively you can also do stars with spikes coming out (more spikes per higher value), I find this the easiest to visualize rather than shape sizes.
I always preferred the blunt "pull this part back to yesterday, when the knot wasn't, move it over here, bring it back to today, and it's unknotted" argument.
There are only three spatial dimensions, and time.<p>If you are going to play tricks using color, you may as well use flavors and odors for a sixth dimension visualization (and any other property you may think of for further extending dimensions).<p>I call bullshit.