While Simic Signet makes colored mana, it isn't colored itself. After all, you can play it with nothing but colorless mana, right? So Ramos wouldn't get any counters from you playing the signet.
If you played Golgari Charm and copied it with Cloven Casting, Ramos would only get two counters. Putting a copy of a spell on the stack isn't the same as actually casting it, and Ramos requires you to cast a spell for him to get the counters.
October 5, 2018 3:48 p.m.
October 5, 2018 4:04 p.m.
When Ramos, Dragon Engine talks about a spell's colors, it's specifically talking about any colors in its casting cost, plus any colors on its color indicator. Simic Signet has no colored mana in its casting cost, nor does it have a color indicator, so it is a colorless spell. Devoid spells also won't trigger Ramos, even if they have colored mana symbols in their cost. Crimson Kobolds will put one counter on Ramos even though it lacks colored symbols in its mana cost because it's still a red spell.
As for Supply // Demand, while it counts as all three colors anywhere else, it's only the colors of the side you cast when on the stack, so Ramos would only get two counters.
October 5, 2018 4:27 p.m.
Additionally fuse cards like Catch / Release only count as a single spell when fused. You'd get 3 counters when casting both halves, not 4, as the overlapping color only counts once. You'd get 2 counters if you only cast one half.