I have a shared Google spreadsheet where several users have already filled out parts. It would be useful to have alternately colored lines to facilitate correct placement of additional data.

Is there a painless method option to alternately color (say, the cells given that already many of them contain text?

In an empty document, there would always be the "color 2 lines, copy-paste 2 lines, copy-paste 4 lines, etc." option, but in the current document, there is already text and some lines are still liable to be deleted which necessitates a recoloring later.