There also was a time when one of my clown loaches was sick, and I was keeping the lights off for much longer periods of time.

Since the illness was a mystery, I kept a close watch on all my fish in the tank for some sign of illness, and I did not notice any improvement in their color either.

When I returned to my normal lighting schedule, I was still keeping a very close watch and saw no deterioration in their color either.

I have never seen my guppies "hang out" in the shade, unless they were giving birth.

I don't mean to do any bashing of Dr. Axelrod either, but DOES he somewhere give you a recommendation as to optimal number of hours of lighting? Did he indicate what diet the fish were being fed? Did he illude to their other environmental conditions?

I ask this because I purchased a book co-authored by him on swordtails, the last 7 full pages are in regards to sex changes in the species.

It goes something like this, "...it's never been proven fully, only partly, and that is if you determine partly to be......... and not.......,and then again it can happen if you consider this to mean..... and that to mean.....,
but once again it's never been proven." "However, one study using female 'B16'showed this........, and another study using female 'C658'showed that....." etc. etc. etc.

"....so if you believe in the Easter Bunny,......"

Let's just say they made me dizzy, and never gave a clear answer.

I am still a firm believer that a healthy, clean, environment, a good balanced diet, and moderation in all things, leads to a happy life.
Guppies included.

As far as color, I'll say it again, see above, and feed some extra spirulina.