It is often tempting to colour a backdrop with our lighting systems - whether it is flash or steady , we have all been fascinated by the business of shining the light through something translucent and seeing what happens on the backdrop. If you pop a piece of coloured glass or cellophane in there you can get amazing tints. Tempts you to just keep one roll of paper on the back and change the appearance from the flash.
Well, if you are using a roll of backdrop paper that is white or very light grey, you may be disappointed with what you get. You can generally see a strong colour when you are setting up the shot but when full power goes through the gel and records on the sensor surface, it can be nearly a complete washout. You see a little colour round edges or where there is some shadow, but very little else.
What you need is a mid neutral grey or even a black. These give some "tooth" for the gel to bite on and depending upon the level of lighting, you can get some very strong colours.
Honl make a number of small gel sets that can be attached onto most speedlights and you can choose Hollywood, Colour Correction, Deep Colour, Autumn...well you can match the foreground mood no matter what it is. They are not expensive, and are the best way to experiment with this form of illumination.
If you need to do bigger lights such as LED panels, or hot lights, you need Lee theatrical gels. These can also be bought in a large set, or ordered in rolls. Generally you have to make your own holder depending upon what sort of light housing is used. It is not hard - my studio has several sets that flop onto the front of Elinchrom lights and the holders are variously 1/8" ply or a couple of sheets of stiff cardboard. There's nothing quite like a hatchet lighting scheme with magenta and electric green to liven up a portrait. Add a smoke machine and a pile of plastic skulls and you have a wedding to remember.
