All tests done in Excel 2007:

So i'm trying to make sense of this particular setting. I understand
the color index has 50-some-odd possibilities, which severely limits
the various iterations of color possible by Excel. So i came up with
the below code, which runs till it hits too many cell formats

Sub colortest()
Application.ScreenUpdating = False
Dim r As Double
Dim c As Double
Dim x As Double
x = 255
For c = 1 To 9999
For r = 1 To 255
With Cells(r, c)
.Interior.Color = x
.Value = x
End With
x = x + 255
Next r
Next c
Application.ScreenUpdating = True
End Sub

I go up in interations of 255 per hex values, but i'm still a bit in
the dark as to why it works this way.

This code works properly for a total of 65429 cells, but then on cell
65430 it says i've reached maximum number of possible cell formats (c
= 257, r = 150, x = 16684650).

Could anyone explain how excel takes a numerical value for the
interiors.color value and determines what the output color will be?