Its nothing to do with light. The brighter the light, the more colourful they are, unless they're greying out. From my bunch I have only one loach that greys out at lights on. The rest don't change colour at all.
Typical ingredients of NLS formula is below. I feed mine a couple of types but mainly Cichlid formula and Algae max. Healthy colour change may take a few months to occur. Don't expect a 3 day wonder once you start feeding better food. For a loach I bought a few years back it took a few months until he started looking like the rest of my bunch, i.e deep yellow and black colours with orange tale. He was very washed out when I bought him. I had a thread here about him but photobucket has deleted my pics and I don't keep them anymore.
Frozen food and most flakes aren't that nutritious unless you have an arsenal of different types of frozen food. I feed frozen food as a treat because they like it, not for nutritional value. NLS is superior to majority of foods sold, if not the best.
See ingredients below.
Whole Antarctic Krill, Whole Fish, Whole Wheat Flour, Ulva Seaweed, Chlorella Algae, Beta Carotene, Spirulina, Kelp, Garlic, Alfalfa, Scallops, Omega-3 Fish Oil, Wakame Seaweed, Spinosum Seaweed, Vitamin A Acetate, Vitamin D Supplement, Vitamin E Supplement, Vitamin B12 Supplement, Niacin, Folic Acid, Biotin, Thiamine Hydrochloride, Riboflavin Supplement, Pyridoxine Hydrochloride, Calcium Pantothenate, L-Ascorby-2-Polyphosphate (Vitamin C), Choline Chloride, Ethylenediamine Dihydroiodide, Cobalt Sulfate, Ferrous Sulfate and Manganese Sulfate.