nothing wrong with shell on. thats whats giving the good color. however you might be carefull with frozen foods. they can put a fish into shock as they do not internally produce much in the way of heat.
Aside from that nice looking arow. you might add some zoe freshwater to your shrimp.that will also aid coloring. Thats all I feed mine and he is looking like this
Dont mean to railroad here, but, You have overflows and that means you have a sump of some kind. why not throw that heater in there, that tank looks awesome and would look better minus a heater.