Lemon was a catalog color for two years, 1968 and 1969. It will often have clear portions in the glass and to me has a “citrusy” look. By “citrusy” I mean that the yellow color is a little green. The lip on lemon pieces often appears to be slightly opalescent.
If you look at the lower right hand side you can see that the lip is a little more green and a little opalescent. Because this occurs only on the lip, when it is present, I assume that it is from the re-heating during fire polishing.