I would like to use Farrow & Ball exterior eggshell paint but the colour is just slightly different to what I need. It just needs a little bit of black to darken the colour slightly. With F&B being expensive I don't want to spend the extra on F&B exterior eggshell black. The 100ml tester pots are based on estate emulsion which will not mix with exterior eggshell (or so I presume). F&B describe the exterior eggshell water based composition as "Based on a 100% acrylic resin" - therefore could I just get a small and cheaper tin of black resin paint and mix it with F&B's exterior eggshell? If so can anyone recommend some suitable black resin paint please? Many thanks for any suggestions.