Differentiate two dimensional image vectors

[shancarter]

When the two grey colors are very close, it's hard to see the two values. A small suggestion:

[thomas-tanay]

I agree, it looks better with a contour. Actually it might be a good idea to do the same on the outer square, as it is sometimes difficult to distinguish from the white background (I used a slightly reduced range of grays to avoid this issue but a contour would make it clearer):

[shancarter]

sounds good.