Spreadsheet Spectrum

I made today's post with Google Spreadsheets.

Here is the original. I used formulas to generate the series of numbers, and then used conditional formatting to do coloration.

My spreadsheet has a formula. This is the first row.

A1
B1
C1
=A3+A1-A2
=A4+A2-A3
=A5+A3-A4
... etc.

this generates a pattern.
1
2
3
2
1
2

The repeating unit is 
1
2
3
2