Relating to where the kratom is grown there is:
Relating to the colour of the stems or veins running through the leaf:
Relating to the grade of leaves used:
One kratom tree can produce both red and white vein leaves. Most kratom on the market appears to be of Indonesian origin. The 'grade' of kratom leaves used is the prevailing factor in determining strength and of course, cost of. Typically the grades will be listed as above, ranging from 'commercial' (the weakest) up to 'enhanced' (the strongest).
As mentioned elsewhere, the quality of kratom will vary depending on where you order it from, and sometimes even from batch to batch. The key is to find a quality, consistent vendor.