Image fill question

[FlexibleLearning.com]

I have a 10px x 10px image. There is a 1px black border with a colour fill.

How do I set the colour fill of the image using an arbitrary RGB value?

It needs to be a mathematical approach setting the pixel data directly
(taking and applying a screen shot of a graphic is going to be too slow).

I've tried all sorts and failed miserably... Can anyone help with this
challenge?

Hugh Senior
FLCo