I am composing an article on the uses of colour in the Hellenistic military right now (relating to the third and second centuries BC, but nonetheless relevant to your mod) and I can send you some information next week if you drop me a line at rubenpostca@hotmail.com .

Short answer to your question: for the period you are interested in, we see linothorakes in purple, pink, red, yellow, and some other colours (Alexander sarcophagus, Aghios Athanasios, some other Macedonian tomb paintings). For helmets, we see them painted in red, purple, perhaps pink (depending on how you want to interpret the colour of the Kinch tomb painting), and blue, though as Etairos has pointed out, this is most likely used to represent iron. The Lyson and Kallikles tomb paintings are probably not all that relevant for your mod considering that they are thought to date to the second century BC.