No need to match, but I like you use up what I’ve got before refilling just 'cuz. If you live in a place with particularly brutal winters (I’ve seen this in Wisconsin and Minnesota plenty, but less so in Colorado where I live now) there’s a purple kind that’s good for melting very light frost, and it’ll better withstand the really crazy low temperatures. But in summer, I like the normal blue stuff to actually clean the windshield.