He looks to me like a fawn, aka dilute red/orange
<A_??C_ddE_ENen> I am concluding this by the first and third photos, in which he has a distinctly creamy cast (I believe what you're referring to as "dusty"). The middle photo, however, looks more like orange. I use ?? in the B spot because there is a trend for red breeders to use chocolate-based colors. He has incredibly clean color, so he might be one of those.
Your question is a good one. Since red is an accepted color in Rex but orange, fawn and cream are not, he could be either a lousy red (aka orange, red without all the plus modifiers, which you can get when you breed a red with another color that does not contribute those modifiers) or dilute red/orange. I usually call the latter color "fawn," but as you note, that can mean something else in a few different breeds (basically low-rufus orange but not dilute, in Flemish Giants; French, English and Mini Lops; and the angora breeds); the other option for a color name for dilute orange would be "cream."
Sometimes, but not always, dilute colored animals will have slightly lighter eyes than their dense colored counterparts, so if his eyes are not quite the dark brown of a red, that might be a clue.
Here's a lousy red (orange) NZ/Satin bunny out of a NZR and a red Satin. The entire litter of eight was this color, so although there was a blue way back on the doe's side, I am almost certain that this animal is not dilute (but in genetics, especially dealing with recessives, I won't say anything is 100% sure
). So you can see that dilute versus simply pale color can be tricky.
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In my experience it takes a pedigree or a test breeding to distinguish between pale orange and fawn/cream. But since I try
not to breed orange or fawn (in Satins and NZs I want red, though obviously I don't always get it!), I don't have extensive experience with it, so I'll be interested to hear if anyone else has any phenotypic clues to distinguish dense orange from dilute.
