The point of pocket squares is that it doesnt really need to match with anything. matching a pocket square to a tie, is seen as perhaps a tad inellegant and the domain of gifts sets from NEXT or TESCO. In a pocket square its a good idea to find something that in its initial colouring or patterning, doesnt really echo anything else you're wearing, but has perhaps an accent colour or tone in it that is picked up somewhere else in your outfit. It could be a small sub colour in the tie, a weave in your shirt or even a fleck of colour in a pair of glasses. I guess what I'm saying is, just pick a material that has a different texture to your suit (probably a smooth silk) in a pattern that doesnt mirror anything else you're wearing. perhaps a paisley.
http://www.permanentstyle.co.uk/2012/01/five-tips-on-pocket-handkerchiefs.html
here are a few examples I like (and you'll see that the PS's pick up only slightly on tones elsewhere in the outfit or dont match at all)
http://individualism.co.uk.s99648.gridserver.com/wp-content/uploads/2008/12/pocket-square-10.jpg
http://3.bp.blogspot.com/-L9SoMwGIBaA/ToCfIAl4oOI/AAAAAAAABbc/0tqgILMRTwQ/s1600/pocket-square_gq.jpg
http://mistercrew.com/files/2010/11/ede_ravenscroft_1.jpg
This on the other hand.. is a NO NO
http://img.alibaba.com/img/pb/951/102/104/1270708688985_us_fileserver2_11848.jpg