the coolant in my 93 ssei appears to be dexcool, in the recovery tank the fluid looks darker than it should be, could my car have been changed over to dexcool and should i flush the brownish looking coolant

Would that brownish colour be oil? When the car is cold open the rad cap and look for oil on the inside of the cap and have a good look in the reservoir. I had this problem on my 92 because the engine oil cooler tubes had a slow leak within the rad.

Another thing it may be is that the coolant when mixed properly (50/50) has enough anti-rust properties not to allow the water to rust the inside of the block and heads. If there is too little coolant then you get rust. At this point you are looking at doing a chemical flush which is a bit of a PITA and requires a kit which can be purchased at any parts store. The instructions should be clear enough to do it but if you feel uncomfortable at all (not properly bleeding system of air after could lead to damaging overheating) have a garage do it and it shouldn't be that expensive.

So first step is to identify what that substance is and even test the strength with a tester (which will let you know if the concentration is too low).

The brown **** is sludge. You should flush your cooling system.

That "brownish looking stuff" might just be GM cooling system suppliment (sealant tabs).

93'* did not have dexcool from the factory, and someone would have had to REALLY flushed it to convert it, and for no reason really. I doubt it'* really dex.

I'll be the optimist here and go with the Dexcool/Green Stuff mix. After all, if you combine green and red you'll get this brown colored liquid. So, I would just flush the radiator (and overflow tank) and put some new 50/50 mixture of water/coolant(green) in your system.