If you want just color, apistos are a better choice, but most times people have better luck with rams as far as hardiness. And as Jan said, we really need to know the tank size to suggest anything species wise. In a 10 I wouldn't add either since you have schools already and likely hit the max fish level in that tank, but ina 20L you could do a pair of rams or apistos. westies like kribensis I really would suggest a 30L unless you know the morph you have is "friendly". I have several species, some kill eachother in well planted 30g! that's with ditherfish too.