Template:Weather box/colp can be used to produce a background color in a table cell, based off a given number. Insert {{Weather box/colp|0}}, with a number from the mm in a 30-day month table above as the first parameter, into a style statement.

Example
{| class="wikitable"
|-
| style="{{Weather box/colp|18}}"|0.7
| style="{{Weather box/colp|157}}"|6.2
| style="{{Weather box/colp|297}}"|11.7
|}

Will produce

0.7 6.2 11.7