Hello KJ6EAD!
I have used different colors of LEDs in different shapes...but in parallel, like in series, I couln't take any ggod result... I mean, when I use one single LED, it gives me 1.5 volts in measure, but when I try to put more then one, it drop so down...I don´t understand why...so I just forgot about using the LEDS for solar cells...I'm now getting better results by making my PV cells from copper chlorine. It is an easy process an is very, very cheap! If you are interested about, I have a good pdf teaching how can you make your own cells at your home. I hope my answer can help you!
---------- Post added at 12:45 ---------- Previous post was at 12:39 ----------
Oh...and about numbers and collors, I found better the green color LEDS when measured one by one...like I said before, when I try to put it together, in series or parallel it doesn't work good...so I can´t say how many you´ll need, becouse I just get good results using them separated...