Normally if I get purple first, I'm at least aware that's what I'm doing. Not this time, purple just happened to be the one that stood out to me first.
Order of difficulty. Yellow is easiest, followed by green, then blue, and purple is supposed to be the hardest.
Purple is also most often the one likely to be something like "starts with a day of the week" or "______ something", types of connections the puzzle creator clearly thinks are the most difficult.