Many times gels are used for creative effect, in this instance i was going for a cool product shot of a black product on a black background.
Camera settings: 1/160 of a second. f/8, ISO 200.
The first product I tried was a speedlight. I Started off with one blue gelled Flash on the back right bouncing off a wall.
I then put another Speedlight in a softbox on the back left with a red gel.
Next i brought in another flash with an (Orange) CTO Gel in a softbox to light the front.
In the end I photographed a few different pieces of Photo gear, I also added a white card on a boom to give some fill from above.
This was one of my favorites from the shoot, but the background was not completely black, due to "light spill". After about 2 minutes in Photoshop I got the result I wanted. You can take a screen shot of the above photo and follow along in Photoshop for the below tutorial.
1) After opening the photo in Photoshop, Grab the Magic Wand tool (W). while holding down the Shift key, click various parts of the background to select it. when your done you should have a pretty good selection around the camera.
2) Alt click (option on mac) on the background layer to unlock it.
3) Alt click on the mask icon to hide the background you just selected.
4) Cntrl click (cmnd on mac) on the new layer icon to create a new layer below the background layer.
5) Press alt+backspace to fill your new background layer with black.
6) you may have some stray spots that the Magic Wand missed so to fix that, alt click on the mask so u can see the mask Preview.
7) Grab the paint Brush tool (B) and paint with white to reveal and black to conceal. Alt click on the mask to return to normal view. and your done!