Hey TREYZX10R I see you have picked the Dragon kit to build. I have been working up to doing this kit myself. I have both the old original Trimaster kit of it, and a more recent Dragon release. As to the decals, if the clear backing has yellowed, yes you need to replace them, BUT if you are taking the off white in the numbers and crosses as a sign, this is how they are supposed to be. The white markings were an off white so as to not stand out quite as much in the dark.
Here are some photos of the decals from my Trimaster kit and the DML kit. Also are the decal sheet and Paint page from the Eduard Fw 190A Nachtjager Limited Edition kit. It is kit 1144 and you can still download the Instructions PDF file from Eduard if you would like. The White on the lower part of the fuselage crosses is covered by the grey of the lower side. Thus you have only the black cross showing.
Would have started myself before now except I needed a paint booth and just finished building it. Here are some photos of it.
30 inches wide with a 22inch indirect flourecent light. 10 x 20 inch air filter to catch paint pigment and 1 or 2 fans pushing about 60 and 120 cubic feet of air respectively. The large parts are an old Monogram B-29 in 1:48th.
Front part folds in a somewhat unorthodox way to make it a bit less bulky. The whole thing only weighs 11.5 pounds.
Like I said it folds up in a somewhat unorthodox way. This was the simplest and flattest way as the light fixture on the underside of the top made things a little tricky.
The backside ducting was built up from acrylic sheet .080 thick. Cut it to size on my band saw and a little file work and sanding on the edges made it easy to glue together with Weldon 3. The vinyl ducting was dryer duct from 1985 (no longer available) but perfect for this application.
The window insert is also from back when. I had a simple 120v brushless instrument fan just sucking the tainted air out in the old days. Couldn't find the fan though I did find all the dryer duct. The duct that was on the back side of that original fan is "COATED" with dried paint, thus the new booth with the air filter.
The other end of the duct hooked up. The white flap over the opening was to keep cold air from flowing back through the tube when the fans are off, and too keep rain from coming into the duct if it happens to be raining out. This setup works extreamely well at keeping the paint fumes around the Zero point everywhere except right at the front of the booth while spraying. I usually can't even smell the fumes while painting.
The booth cost me about $120. Will have to go and do a pricing of the separate items to know for sure. The fans are 12V computer fans and then a 6 amp 12V power supply to run them (overkill I know but it was a LOT cheaper than Radio Shack) The light fixture was about $10, the fans and supply were right at $40. The 1:8th inch thick Masonite was cut from a 2ft x 4ft sheet I picked up at Home Depot. The acrylic and aluminum extrusions were bought at Lowe's. If you are having to do your painting out in the Garage or worse OUTSIDE 
This might be a good way to get the spouse (if you have one) to let you paint inside. After all her main complaint is the smell so, if there is no smell there should be no complaint. 
