Here is my little chime.
To achieve a good depth of colour from a dot-matrix print, I print two or three copies of the required decal and when positioning it on the model, I then overlay it with a second decal to get a better depth of colour. If white is involved, then I use white backed decal sheet, but then the overlays are printed on clear, therefore only the one white backed decal has to be neatly trimmed and if you do by chance nick a bit out of the white backed decal, the full clear backed overlay decal will cover this glitch.