Bamboo shrimp can change color as they age. It is normal for them to be brown, tan, maroon, and lighter red. It's a good idea to have a power head pushing water inside the tank. The current helps them to gather food more quickly.
I'm currently down to one bamboo shrimp. He's getting old, close to two years that I've had him, and I don't know how much longer he'll last. At first, my bamboo shrimp tend to have light color, likely due to stress of capture and handling. They usually darken and either take on a darker brown, or red color.