DOT 5 or silicone brake fluid is usually dark amber or purple color as manufactured.
DOT 3 or 4 Glycol brake fluid is nearly clear when new. DOT 3 or 4 will also turn dark as it absorbs moisture and needs replacing.
DOT 4 has a roughly 40 degree higher boiling point and is 100% interchangable with DOT 3.
If you contaminate and intermix DOT 3 or 4 Glycol brake fluid with DOT 5 silicone in any amounts the brake system should be completely and thoroughly flushed or best taken apart and the rubber parts replaced with new.
I run into Hmmm....what type of brake fluid is in a old car brake system in my work.
I take a small sample from the car and drop it into a clear jar with new DOT 3 or 4. If it sits as a ball or jelly bean in the bottom of the DOT 3 or 4, it's DOT 5 silicone.
Be sure of what fluid type is in your old cars brake system if you are not sure. Most old cars still have regular glycol DOT3 in them.