Transmission fluid is red (different from engine oil's amber/brown). A red spot on your driveway under the front of the vehicle indicates a transmission fluid leak.
Common leak sources: pan gasket (cheapest fix), transmission cooler lines, output shaft seal (expensive), transmission case crack (most expensive). Each source has a different fix and price.
Low transmission fluid causes shifting problems — slipping, delayed engagement, harsh shifts. Continued driving on low fluid destroys the transmission internally. Replacement cost runs $2,000–$5,000+.
Check fluid level via the dipstick (if your vehicle has one). Many modern vehicles eliminated the dipstick — check the level via dealer service or a shop with the right tools.
If your driveway shows red spots, get the leak diagnosed within a week. The cost of fixing a leak ($200–$1,500) is far less than the cost of a transmission replacement.