The color of antifreeze is no indication of the quality or of what it is made from . Some brands are pink, some green, some blue the basic ingredient is colourless the colour is just a 'brand marker' remember the old paraffin ? there was Green, blue and pink but it was all the same stuff just a diffrent dye. antifreeze is the same the colour is just a dye .
If you want to be really safe you need to test the pH of antifreeze to see when it has turned acidic. ( pH is a scale of acidity ,1 is very alkaline 14 is very acid and 7 is neutral, pure water is 7pH , water in rivers lakes etc is from 6 to 8 pH) New antifreeze solution would be 6 to 8pH if the pH went above 9 then I would say it is time to change it. The pH of antifreeze (as I said) rises due to the absorption of acidic exhaust gas a pH of 9 to 10 is the point where the anitfreeze is starting to be so acidic that it may damage the engine and it should be changed. I actually find it hard to belive that a modern car like BMW mini has acidic anti freeze unless it has done over 100,000 miles without the radiator being drained and refilled with new antifreeze. It is normally recomended to drain and refill the radiator every 75,000 miles or so.