Dr A, I've seen then almost that blue and redish/brown.
What temp is the betta at? shrimp dont like over 26 deg and will have to be acclimatized slowly from the probably chilly 10-12deg of the stream.
sup42, you can catch them during the day with a sturdy net pulled through weeds/grass/cress etc in the stream but they are easy to see at night as their eyes glow in the torch light