Well, it used to be that all Merc (and G-05) coolant was yellow, back in the late '80s. It also used to be that all Dex-Cool was reddish and all normal coolant was green. It just ain't so anymore. The color is from dye, not from chemical composition, meaning that manufacturers can use whatever dyes they like. The most common colors for G-05 coolant are yellow and red, but it doesn't surprise me that Merc coolant is, or was at one point, blue. I bet it's G-05. Read the label and it'll tell you. Look for the ingredient "glysantin" or the acronym HOAT (Hybrid Organic Acid Technology) or the spec G-05. What I DO know is that when Tom Townsend recommended Merc coolant in the early '90s, it was the only G-05 spec coolant available in the USA. So what he recommended was, in effect, G-05 coolant.
All you need to know about mixing is that you can mix G-05 and normal coolant indiscriminately, and you should not mix Dex-Cool with anything.
By the way, you bear an uncanny resemblance to a certain singer from New Jersey. I'll bet you get confused with him all the time!
It's been remarked that I look like the Boss, but only when I have suitably long hair and a dirty enough shirt...