annotate with two different colors based on threshold

I added the capability to annotate an image with features of two different colors. I found this useful for playing around with cutoff thresholds. e.g. see how many features you miss if you increase the minimum size.
This is to handle the case where someone puts a single number in as a threshold rather than a list. It must be converted to a list because later split_thresh[0] needs to return a value. Possible split_thresh: [10], 10, 10.0, [10,12,13], etc.