Getting the perfect transition of two colors on one wall

How do I create a straight, exact transition between 2 different colors? With the right technique, it can be quite simple.

The right material: For coarse substrates (such as ingrain wallpaper), we recommend using a special adhesive tape for a clean color edge and, for very coarse plaster, possibly sealing the edge of the adhesive tape very thinly with acrylic beforehand.

Step 1: It is best to start by painting the area of the later a lighter shade. When this is done, let the paint dry thoroughly before proceeding to the next step.

Work step 2: Now mask-off the area for the second darker shade with the tape, paint over the edge of the tape at the transition with the first, lighter shade and allow to dry again. The lighter color now runs under the tape and seals it. Since it is the same shade, this will not be noticeable later!

Step 3: Now you can apply the second shade to the desired area as usual and then peel off the adhesive tape. For the following colors, be sure to do this while wet:

Farrow & Ball Modern Emulsion
Little Greene Intelligent Matt Emulsion