You hit platinum at 250. I have 1696/1726/1648/1736/1828 with 1281/1444 cards mastered. Color mastery as a mechanic is dead after platinum.
@ElimGarak Have you ever broken down your card collection on a spreadsheet and calculated your points? I could be higher than what is shown in your profile. Back when the Terror in the Shadows first came out I could not play the first few cycles because my mastery points were blocking me. The solution was to dock each color category 500 points, but they never put it back.
@tfg76 I like collecting, and since you can't collect the cards I collect mastery points. Plus its a way to grind out runes and catch a glimpse of how each card works.