From the way your question is worded I'm guessing that the sight glass isn't normally red color. It sounds like you are saying that it looks like something has dyed the sight glass red.
If that's so....well, this is just a guess....but are all the other tractors you are looking at with the red sight glass used tractors? The reason that I ask is it used to be pretty common practice to mix ATF with the hydraulic fluid - there are even some folks who still do - especially in the winter or real cold climates. And ATF has a stong red dye.
You'll get the full range of opinions on whether mixing was a good thing to do or not. BTW, it wasn't done to save money; ATF tends to be more expensive than most hydraulic fluids.
Now that there are more reasonably priced low viscosity hydraulic fluids and even some reasonably priced synthetics I imagine the practice will die out.
rScotty
I don't know anyone that puts dye in unless they have a problem and are trying to locate a stubborn leak. Could the factory?
I used to think on the same lines but the DPF systems can royally ruin your month. All is fine and dandy and then the day you don't check your oil your crankcase and it is overflowing of carbon and fuel.... or worse, coolant. Happened to me.The funniest thing about this is the people who put the least hours on machines are the ones who worry the most about stuff like this. Little CUT's who live in the garage and get 20 hours a year of easy use while the owner changes oil every year because the manual says to.
These are the machines to look for if you can find them used. Probably have 100-200 hours and the owner finally got sent to the nursing home or dies and the tractor is in pristine condition with barely a scratch. Most implements are barely used and it's had 9 oil changes in 123 hours of use. LOL