Help needed with REGEX matching

Yahoo Pipes: Query about 'Matches regex' in Filter:

I am trying to create a filter that returns a match if it finds two or more occurrences of particular substrings from a set list (either two or more occurrences of the same substring, or a single occurence of two or more of the substrings in my list). So, if my list was "red", "blue" and "green" (it actually has more items), I would want it to return results that would be the same as those from the BOOLEAN search:

(red AND red) OR (blue AND blue) OR (green AND green) OR (red AND blue) OR (red AND green) OR (blue AND green)

I also want the search to be case-insensitive and to include derivative words (e.g. "reds", "greenish", "bluegrass", etc.)

Precisely what would I need to type into 'Matches regex' box to obtain this result? Reading various (mainly quite confusing) tutorials online, I came up with "(item1|item2|item3){2,}", which didn't seem to work,despite me trying different types of brackets/no brackets (they varied in the tutorials I looked at) and putting the individual items inside quotation marks (or not). Where am I going wrong?

Can anyone help this struggling regex newbie?