Photoshop CS5 color help.

Question

Hey, I tried figuring this out myself but to no avail. so I am asking anyone here for some advice.
I am trying to make a "lightsaber" effect on some images. In an earlier version of photoshop (earlier than the CS versions i think) it ended up as the blade with its color on a black background. This image was placed on top of my image, the blending mode changed to screen, and it turned out fine. The black disappeared, and the blade kept its vibrant color.
Tutorial I used: http://alienryderflex.com/rotoscope/
Blade image before "screeining" over background image: http://i447.photobucket.com/albums/qq192/CrazedOne1988/lasers.jpg
I've tried this in cs3 and cs5, but something in the program must have changed. When I set the "blades" image to screen, the blade color ends up blending into the background color (altering the blades color) and ends up completely disappearing against a white background. The blade color alters based on what color the image behind it is. I want the blades to keep their vibrant color regardless of what background it is against. Any advice?
Pre-CS: http://i447.photobucket.com/albums/qq192/CrazedOne1988/endoftheworld.jpg
CS3 CS5: http://fc09.deviantart.net/fs37/i/2008/284/8/1/Halo_Star_Wars_by_CrazedOne1988.jpg (blade color in this image was set to Red:0 Green: 127 Blue: 255, a clear cyan blue color, and it's blending into the orange, creating a purplish blue color)

Answer 1

When I set the "blades" image to screen, the blade color ends up blending into the background color (altering the blades color) and ends up completely disappearing against a white background.
Of course they will disappear against a white background.
The Blending Mode Screen can only produce lighter values (you can figure out the math yourself or check out the Help, »Blending mode descriptions«) so on white it will result in white.
Anyway, I guess the intended effect may possibly be approximated with Blend Mode Normal.
In the case of your example a Selection based on Green used to make a Green (0/255/0) Solid Color Layer, a Selection based on either Red or Blue as the basis of a white Solid Color Layer could be used.
On Black the results are identical, on lighter backgrounds the result will differ increasingly, but one can still control the aura via Opacity.