Harry, in most cases, the effect will "pass". However in your case.... I suspect your farts will always have a certain odd lilt.
What happens is the selenium, and other chemical components are absorbed and have a really easy time making into your bloodstream. The effect will wear off as the selenium is excreted. Might take a day. I always got popcorn farts when working with it.... just saying. And the same holds true for 44-40 and Outer's and Hoppe's gun blue products, which are all just similar formulations.
I am not a chemist, but paid attention to a certain extent in chemistry classes. I know certain components will naturally "plate" with no electrical current needed. Copper on steel is one of those. Selenium on steel is another. I'm trying to recall the experiment, but I think we took polished steel and a real penny and stuck 'em in vinegar and the steel got copper plated. <--- don't crucify me if it was another acid, or a acidic salt compound, it was only about 50 years ago since I did that. Yah, I'm old.
Anyroads, that's what is going on with Oxpho or any of the "cold blue" compounds. Here's the rub... you can plate the steel with a thin layer of selenium, and there is a mild acid in the product that slightly etches the steel surface. You can then "polish" out the selenium a bit to restore the smooth surface that was etched. The smoothness is the thin layer of selenium.
As Brownell's says, if the color disappears on subsequent applications, you've used too much chemical. Right that is, because the acid has wiped out the selenium that was on the steel. (popcorn fart time)
Wear gloves, eye protection. All of those are not life or death if touched, but... not the best for ya if you're using them over and over again. An occasional touch up on a front sight or something... ya know, big deal. You're trying to do something bigger (which generally will tend to be spotchy unless you spend a LOT of time with it) then glove/glasses up.
On another note, I once bought a used "blue" 4" Python from a guy. An occasional customer to the range. It looked like hell, and I gave him, from memory, about $150 for it. Turns out it was done in cold blue. You can always tell cold blue because it will rub off fairly easily with rough cloth (aka burlap or rough muslin). And it stinks when you rub it off... like your selenium farts will. That was an interesting piece. I never worked on an old Colt revolver action. We just didn't get that many of 'em into the shop. The parts were available, and this Python was way out of time. So I sat and studied, and with the addition of a hand and a little fitment here and there to the other parts.... and let me tell you, there is an _order_ that must be followed when fitting the lockwork... it timed up nice. Shot ok too. So... it went off to have matte hard chrome put on it. I used Accurate for that, they did good work. It came back, and it was dead flat, no shine anyplace and everyone said it looked like it was made from putty. It did! I played with it for a while and sold it for a slight profit (considering the plating job). But here ya go, an entire Python "cold blued".... no accounting for the tastes of some folks.