If I am not imposing, I would also like to add or include some tips from another painter's point of view when it comes to painting different colors ; If you are not
using a base paint from the beginning , then you don't have that same color to paint a guide line down your tape edge. In this instance you can use:
1. using a clear matte acrylic sealer works great.
2. using a clear acrylic glaze with driers already in it works great.
3. using a non glare matte or low sheen varnish works great.
4. using the correct or "my" correct tape works great (scotch 3m delicate blue painter's tape 2080).
5. burnish the tape really good. I use my index finger and press really hard. Using tape knives, etc. need to be careful- may accidentally get a nick or gouge in the tape . Popsicle sticks, old credit cards you get in the mail are good to burnish with also.
6. don't brush or roll the sealer (or your paint) up against and into the taped edge line. Just takes a little thin line down the middle of the tape edge. Brushing or rolling up to and against the tape line could cause seepage and force paint under the tape edge. Brush or roll down over it ; doesn't need a lot of pressure to seal or even painting with your selected color.
7. works best on smooth surfaces. If you have textured surfaces, you can also do the above, but may need to have an artist brush handy for touch ups.