So far Des, it looks like you have been getting the right answers.
The colour is Silver Green, same as my Crayford wagon was, (see other postings for more on that). Often called Thistle Green but that came later, I have an original colour chart which confirms Silver green for the earlier ones.
The brake warning light on yours should be just for parking brake on or fluid low, and if a top-up cured it, you now know, but yes, as stated above, brake fluid can not just evaporate, so you have a leak.
The difference between min and max on most brake fluid reservoirs is the amount neede to go down the pipes to compensate for pad wear, so when it is on min. your pads are probably worn down.
The only other cause is definitely a leak.
Easy to see if the calipers or hoses are wet, but a common culprit is the seal at the back of the master cylinder, so if there is a damp trail under the flange down the front of the booster it is a master cylinder rebuild.
It is always worth flushing with fresh fluid when buying a car with unknown history and then every two years, brake fluid is hydroscopic, meaning it absorbs water from the atmosphere, and the higher the water content, the lower the boiling point, and then one day going down a mountain the pedal will go straight to the florr, I know, I've done it!
All easy stuff to fix though, so it still sounds too good to wreck. Give it a service, brake fluid, oil change, plugs etc, then drive it a while before deciding. It may turn out to be a good daily driver.
Regards,
Chris M.
