This is probably a simple answer, but I cannot see it.

I have four cells, A1, B1, C1 and D1. What I would like to do is to have a
funtion so that when values are entered into A1(Red), B1(Green), and
C1(Blue), the interior color of D1 would correspond to the RGB values
entered.

Is there such a beast where I could type into cell D1, =RGB(A1, B1, C1) ?
If not how would I go about creating such a function?