I did use the search function but could not quite find the answers I needed.
So the deal is I got a new girth. It GOREOUS. Soft, beautiful leather, not stiff at all, I love it. I had two color options, Light brown (kind of like an oakbark color) and a very dark Havana. I went with the Light brown because my saddle isn’t quite as dark as the other tone and I figured I could darken it. Well, I used the girth today, fit well, but I noticed once it was on it was definitely going to need some darkeing. So I took it home and tried Hydrophane darkening oil. No luck, after letting it sit for a while, so I wiped the excess off. I then warmed some olive oil up and applied it liberally. It has been sitting for several hours with no signs of darkening 
I think the main issue is that the leather is just refusing to even absorb the oil- it’s all just sitting on the surface. I know this is often the case with cheaper leather but this leather is nice. Maybe there is some sort of seal on it, but I haven’t noticed anything waxy and I’m too afraid to try anything extreme to try and remove something im not even sure is there.
Sorry for the essay, help me COTHers! I’m desperate because I’ve already oiled it, so I doubt I can return it (not that I really want to, because its so nice) and I really want it to look okay for the bigger show I have this weekend.
Hydrophane is useless for darkening, IMHO.
The best way to darken leather is to let it sit in the sun somewhere (or use an oven, low heat - 150f for 5m works for me) and then apply warm olive oil (microwave 1c for 20s or less depending on microwave wattage).
Your new girth likely isn’t absorbing much oil because it’s been aniline treated and currently, likely doesn’t need the conditioning. If you put it in the sun or somewhere warm for a while, it will help break down the waxy surface which will promote the oil sinking into the leather - the warmth seems to open the pores, so to speak.
Additionally - you don’t want to saturate the leather - not only will it make it ‘reject’ the new oil, it will also weaken the collagen/fibers in the leather. It’s better to apply in small amounts repeatedly, and in my experience, makes the darkening process go quicker because you can apply more over a shorter period of time. If you saturate your leather in one go it can take weeks for the leather to absorb or expell it.
If you’re really desperate and want to nix the wax finish ASAP, you can do a soft mixture of acetone and water - I do about 1 part acetone to 3 parts water and swab with a cotton ball back and forth - you have to make sure 100% the application is consistent and even and wash immediately with something like glycerin or castille soap. I personally prefer the castille - it tackifies the leather and is very good at removing solvents and dirt.
Although, you aren’t going to see a huge difference in just one application. Darkening leather is a multi-step process. I usually will span it over a few weeks - clean w/castille and oil w/olive after a ‘sunbath’, use a few days, clean w/glycerin oil w/neatsfoot, use a few days, wipe clean w/ tack sponge condition w leaderbalsam, use a few days. I find rotating the products addresses various things the other products don’t - IE, castille is great at removing embedded dirt but really dries out the leather - olive oil is excellent for darkening but dries out quickly - leaderbalsam traps in moisture and conditions, etc etc.
I like the Walsh/Blue Ribbon oil for darkening, it has a little stain in it, and really helps darken quickly, although I agree with beowulf that darkening is an on-going process, don’t be in a hurry. As you ride, clean, condition it will start to darken, unless, as you suspect, it has some kind of sealant on it. I would try castile soap on it before you oil again to try and remove the sealant, others would suggest ammonia but I prefer castile.
You can soak in dark coffee- although not for too long as it’s very drying
Clean the leather with Effax leather combi or my trainer who taught me this trick… Used Murphy’s oil. It cleaned all the leather"sealant" they put on. Make sure it’s cleaned good on the edges. Then soak in peanut oil. The longer it stays the darker it gets so you can control the color. I had a girth from Dover that was oak bark and did this it turned out a beautiful color lighter than Havana but still rich and dark. I left it overnight and maybe another half day in an airtight container. Don’t drowned it but pour like an inch in and shake the container with girth in it so that it gets good and covered. Then leave overnight. Then repeat if you want darker. Be sure the oil is spread evenly. It doesn’t hurt the stitching either.
This is also what Edgewood recommends to darken their tack.
I just darkened a CWD bridle with hoof oil (the kind that is bad for their feet, we keep it around just for tack.) It stained it beautifully and left it really nice and soft.
