Now I see.It is true the Revell paints are condensed.But you have to use an enamel Revell thiner or Humbrol one ( for oil enamels or acrylic ones I don't know which kind of them you use) to dilute the paints.If you use an airbrush the colours have to be much more diluted.As far as their colour tonality is concerned.The best way to see what is a real colour of a paint you have, before you start painting of a model of course, is to use a sheet of white or light grey cardboard and paint the enamels on it.It doesn't matter what is a shape of painted areas, they can be boxes or stripes,but it is important to paint quite big ones ( 6x4 cm or so so).When the sample is dry ( you can use a hair-dryer to dry it faster) you can compare it to the one in the pics.If it isn't you can add a drop of white,black or others you need to make the proper colour tonality.And compare it again.You can repeat the procedure as many times as the colour tonality will be the one you need.That is all about the manual method of obtaining colours.Certainly the easiest method of this is to buy enamels of other firms :Gunze,Xtracolor or even Humbrol.But I should you warn, even in the case you can be discontented because in the pictures especially in these that were initially black&white and colourized later the colours can be different from reality.