Trying to find some suitable software, any ideas?

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graphics

programming

I want to find some software, ideally freeware, that can represent numbers i enter into a grid as colors from a varying scale. I would also like to be able to draw a basic black outline on the grid as well.
The aim is to provide a way to display moisture readings in a section of wall. So different colors would indicate differing levels of moisture eg red being very wet and green being dry.

So I would like to draw an outline on a grid, enter numbers into grid squares, the square is then filled in a corresponding color.

Im wondering if anyone knows of any software similar to this? Or a C# program that is similar I could modify? :-D

Thanks
Van