Car is an '89 245

This is an addition to my previous post about PS fluid. I forgot to ask about what type of ATF to add when the fluid type already inside the PS resevoir is not known. The fluid in the resevoir is pinkish, so I assume it's ATF. The question is I don't know what type it is. I have Type F and Dexron/Mercon III in my house. My archive search came up with bricknuts using either of the two ATF. But what if you're adding fluid to the PS and don't know what the current fluid type inside is? Which one should I use? Is it okay to mix should I happen to add Type F to a PS resevoir with Dexron III and vice versa? Thanks in advance!