Didn’t see any differences in the body, but in the mechanism inside there are some differences. Here are some photos comparting them side by side (on the left is the white sticker version and on the right is the yellow sticker one):
The length of the tube on versions with the lead hardness indicator is greater than that of the earlier versions. I didn’t measure it with a ruler, but it should be around 1cm. Despite the tube being longer, they are interchangeable; if you put the tube from the newer models into the older models, it works normally, and vice versa.