need help with gels on non-paper backgrounds

Mesmer wrote in post #15475291
That's what I would try next. Move your gelled light further from your background (and/or zoom the flash our as much as possible). It looks like you have the room, so experiment with just your gelled light until it fills as much of the frame as you're looking for.

Okay, to be continued tonight. I think I'm moving in the right direction. Now that I know that I need to control zoom in manual flash mode, the pieces are starting to come together.

On a related note, the gel I was using (Follies Pink) was from Rogue. Only problem is that the background isn't really pink but more of a magenta. Is this because of the black background? Should I expect something closer to pink when I use a grey background? I want a pink background (similar to the pink on the Minnie in my shots) for photographing my daughter who is 15 months old. Should I consider going back to gelling the white background now that I know my issue was with the flash zoom? It appears (from the 1st photo) that my main light and fill light are not spilling onto the background, or is it just an illusion?

I experienced the color becoming lighter the higher my flash output was, as gonzogolf mentioned in post #3. You might be able to get a more suitable pink color by increasing your output power thus desaturating the color a bit.

gonzogolf wrote in post #15471840
On the othe hand, you can turn the gelled flash up too high and it essentially desaturates the gel. Try it at varying powers to see what you end up with.

gonzogolf wrote in post #15475307
If you cant move the flash any farther away from the background perhaps try adding a bounce card to increase the spread pattern.

Problem with that is it'll rob most of the power. To get a gelled flash unit to compete with studio strobes you need to fire it direct.

Theoretically, a flash zoomed to 20mm will cover an area 1.8x wide and 1.2x high, where x is the distance to the target (at a 90 degree angle). This means from a distance of 3 feet, it'll cover an area 3.6 ft. x 5.4 ft. on the backdrop. You'll never get even coverage by aiming it up at an angle (can't get around the inverse square law), so increasing the distance will allow less of an upward angle and help with that aspect, too.

If you really want to color a larger area then you need to get it further from the background. Also I'd recommend no more than 1/2 power on the gelled Speedlite. This will give you a workable recycle time and reduce the chance of melting the gel.

Of course the combination of greater distance and a lower power setting will require that you adjust your aperture and other lights accordingly.

But I also think you should reconsider the need to color such a large area. I generally use a snoot on mine to create a nice vignette behind the subject.

I think I was at 1/4 power on my 430exii for this shot. It started to lose it's rich color when I went higher than that. So I adjusted the distance to the wall as needed. And yes, a nice vignetting will occur when the light is more focused. I shot this against a white wall FWIW.

Are you still using a gelled speedlite, or are you using a larger gelled strobe?
While your test shot did a nice job getting the entire BG purple, I think Curtis has a good suggestion in trying to control the BG illumination pattern a bit more.