Tranny fluid change question

[dlboltond]

I have a 1992 Maristar 210 with the velvet 1:1 transmission. Bought it end of the season last year and am trying to catch up on maintenance. I went to look at the transmission fluid and this is what I found.

The picture makes it look a little darker than it really is. My question is what can I put back in the transmission? I can't tell if this is motor oil or transmission fluid or does that even matter? Can 15w40 be used in the direct drive transmissions? I can not see any trace of red.

My plan is to change it 2-3 times this season until it cleans up.

Thanks
D