[reynard]

Tocopherol, as you said, has a yellow color. However, tocopherol acetate is colorless and show same function.
In addition, there are various antioxidants you could use, most notably BHT and BHA.

I think it would be good to consider these as well.

[reynard]

Aside from the main question, To identify these two types O/W and W/O, place a drop of emulsion on a microscope and bring it into contact with a drop of water or oil. If it mixes freely with water, it is classified as O/W type. If it mixes easily with oil, it is classified as W/O type.

It would be a good idea to first use HCl as a pH adjuster, and then try various pH adjusters if there are no problems at the desired pH of 6.0. ex. citrate.
Alternatively, it is possible that Citrate was manufactured at a low dilution of 10-20%. Since it mixes with water 1:1 to some extent, I think it would be a good idea to prepare a 50% solution and then use it.

[reynard]

Not only UV light but also visible light can have an effect. Therefore, I think it is necessary to shade the product.
And is there anything that uses antioxidants? Since Vitamin E is itself an antioxidant, I am curious as to whether antioxidants such as BHT or BHA were used to use it as the main ingredient.

[reynard]

What you said is correct.

It is true that α-tocopherol acetate is physiologically active only when take it oral.

Thank you for your correction.

[reynard]

Assuming that the product is sealed well from air, light have had main reason.

Also, tocopherol acetate has a lighter color, so it would be a good choice, if u could use it.