If i read your post correct the artist would like to have a screen for each color? so there would not be any blends if you had a bigger press. For me I would blend red and yellow to get an orange, that royal blue and yellow to get that lime green and maybe a touch of that light blue or black to tint that off white color, if I'm correct that's 6 screens leaving you with two screens open if a color don't work out, this should work doing a sim process with some regular inks. I'm sure some others will give there best advice and trust me there are some really good sep guys here that know colors and I'm not one of them LOL, just giving my 2 cents