The base of your model is not aqua but light blue. Perhaps it is time for a comeback of this picture: Mick Stannard lists three different variations of the towing bracket, the first two of which are very similar. Both are not accompanied by a rivet, the first one has a rounded foot, the second one a square foot. The third type is the one with the rivet, the towing bracket being of a completely different design.

Light blue, aqua, dark blue and pale blue bases.

Light blue bases exist with all three types of towing brackets, aqua (sea green) bases are only found with the first two. A dark blue base is only listed with the second type, which means the third example shown above is actually mid blue rather than dark blue (sorry for the mistake), for mid blue and pale blue bases exist only with the third type of towing bracket.

Light blue is by far the most common base color on this model, all four others are fairly scarce.

The 1-75 Regular Wheels produced by AIM -1st printing 1976 has small cutouts of the casting variations which are extremely helpful in understanding what to look for.