Tangerine seems to be in several finishes but I can relate to three that come to mind that are all considered Tangerine. The pieces pictured are what most collectors see Tangerine comprised of a red/orange fading to yellow or amber coloration. A second variation is a dark red stopper/neck/top fading to almost clear or pale amber color. The third that is also Tangerine is where the piece is a reddish orange being very vibrant in color but the whole piece is close to being a solid color without any variation. You can go back into the August blog pages to see just such a photo I took of several crackle pieces in Tangerine. I do have a small footed ruffle edge vase that is bright orange in color. I am not familiar with the technique that causes the variation or fade but hopefully someone more knowledgeable will take this chance to educate us both.
The red orange only variation is generally early tangerine glass and the coloration of those pieces differs from current pieces due to the batch formulation. There have been a number of batch changes through the years due to chemical availability and safety measures. The other color variations are due to the way the piece is worked in production (i.e. The amount of time it is heated in the glory hole, how long it takes to go from production to the lehr, as well as various batch formulations). I will speak with Randy and see if he has anything to add.