I use Dullcote without probs even though it does appear to soften the acrylic paint. As long as you do not touch it until dry, it settles down fine. All top coats will darken light colours and lighten dark colours, if you want to, then lighten/darken the base colour when spraying to compensate.
There are several old threads in the forum in regard to using Future and Tamiya Flat coat with great success. You need to mix Future and Tamiya Flat at 50/50 ratio or more flat, but an effective satin finish for modern vehicles can be obtained by varying the mix as well. The trick with Futureand Flat is to do very light coats, each allowed to dry before the next, not one heavy coat. One heavy coat will usually go white and leave an effect like ice on the vehicle. Try doing a search using Future as a base search word for more threads; also check out Swanny’s ‘sticky’ thread on Future in the techniques area.
Just be careful with the decal setting agent you use. Mr Marksoftener can sometimes react with Future and make it go a cloudy white. Test your decal softener on a scrap piece of plastic that has been sprayed with Future first.
Here in Australia Future was marketed as ‘Pledge -one-go’, but the formula has been changed and does not work any more - I know from bad experience[V].
I use Polly Scale. I tried the Future and Flat once, and it looked like somebody frosted the parts. On the other hand, whenever this comes up, I seem to be the only one who never seemed to make it work.
the testor clear coats from the spray cans are lacquer based. you will have to allow the acrylic paints to dry entirely before applying those so they don’t screw each other up. I use Testor’s acrylic dull coat over their enamel line of paints.