Ethel glycol was used in antifreeze for a long time, so was methanol. However, most antifreezes are now propylene glycol, as its less toxic to humans, animals, and plants. You can mix Ethel glycol and propylene glycol without any major adverse effect, you might see a couple degrees higher engine temps, but a few degrees is nothing. I'd suggest draining all the coolant anyway, coolant goes bad over time, its additive packages wear out and the coolant becomes acidic.
Dexcool is a silicate based antifreeze, if you mix 50/50 Dexcool and a glycol, then you will start to see problems. As long as you react when the temps start to go up, it won't cause lasting damage. If its that low you should be draining it anyway, not just topping it off. Mixing a few cups of Dexcool with a glycol will not cause any harm, neither with a few cups of glycol in Dexcool.
Colors are also relatively misleading, tI've seen so many colors of coolant its getting stupid. I've seen Red, Orange, Yellow, Green, Blue, purple, all in good condition. I'd never recommend Dexcool to anyone as it has much higher service requirements, you have to check it every year to make sure its not becoming acidic.
Chances are, if they put Orange in, they didn't drain or flush it, so whatever harm has been done, is already there. Just go get some Universal antifreeze and flush the system with a garden hose if possible. it contains all the additive packages you need. The Term "Universal" is only misleading if you don't know what you're reading, which can be misleading. Its like saying math is easy if you know how to do math, so I cant fault anyone for not knowing. The universal is not talking about compatibility with other coolants, its talking about compatibility with vehicle manufacturers, as it contains all the additive packages required by all auto manufacturers in the world. We use Universal antifreeze at work and it goes in everything from Chevys to Jaguars.
