What does blue to red mean exactly. We need to know what kind of blue light were you using, a floro or a MH? If you went from floro to HPS, you shocked it with too much light, not the color. It isn't really necessary to switch light either, HPS does fine to veg. Acclimate plants that were under floros to HPS 3 feet away and slowly lower them. The light is extremely strong in comparison. You'd get the same results by putting a plant that was under floros outside in direct sun, the sun is so much stronger, it'll just kill them. Get the light up as high as you can and it should perk up in a day, or better yet,go back to the floros till it perks and then start 3 feet up with the hps when it looks healthy. If you were by chance using a MH already and it did this when you switched to HPS, don't know what to tell you, people switch spectrums all the time. There's no way to half change a bulb. If this is the case, your looking at a different issue than light.
In the future, just veg under the HPS, it'll go faster than the blue floros...unless your trying to save power.
