You can paint the cover to the outlets and light switches and the vent and return covers. However, the switches and the outlets themselves are trickier. If you don't have a lot of them, you could replace them with black switches and outlets. I was in the same situation with a brown room and I left the switches and outlets white. It just didn't bother me enough to change them. For the air vents and returns, instead of painting them red, you might want to spray paint them with black enamel. Spray enamel is less likely to drip and clump in corners.

You can also temporarily convert any screw-in lamp base, such as one or more of your floodlights, into an electrical outlet with a screw-in outlet, like the one attached. It's not the most elegant solution, but it works and would be very inexpensive. Something to consider since you'll only be using them for a few weeks per year. Here is a link that might be useful: Screw-in outlet

You didn't accomplish anything by removing the break-off fin located between the black screws, and then tying them back together with wirenuts. Because it wasnt done at the power source hot. Marco, you need to think three different animals here 1. the power source 2. the three way switch circuit & lights 3. the solo outlet First task is to find the original hot. For you to keep both the 3 way switch and have a separate outlet, the outlet needs to be located in the box with the original hot OR a separate wire needs to be run to supply independent power to the outlet in the second box. The 3 way switch wiring is its own animal and cannot include the outlet if you want the outlet to not be dependent on the switches. You can't use the traveler as a constant hot unless you get rid of the 3 way. If you got rid of the 3 way, you would use black for the single light switch and red for the outlet hot.

I thought I replied to this post earlier today, but I guess it did not go through. The wiring for the receptacle and the light beyond it sound similar to what I have run across a couple of times in my house. If the power is running to the light switch, then they may have run 14/3 from the switch to the 1st outlet and used the white/black pair to power the receptacle, and the white/red pair passes through the receptacle to provide power to the light that is beyond. The only odd part is that usually you only need 14/2 from the receptacle to the light to make this work, but you said they had two reds nutted together in the box. You can use a similar scheme in reverse if you have power at the light, then 14/3 from the light to the receptacle, and then 14/2 running to the switch. The red wire is just used as a traveler that passes through the receptacle to provide a switch loop from the light switch to the light. I was very confused the first time I found this type of wiring scheme, since it looked like I was working with a 3 way switch circuit. However, it seemed that it was just a way to save running one more 12/2 cable from the light switch to the light. Bruce.