If white spots remain on the glass after the fuel has burned out, this indicates that there are no impurities in the fuel. And if the spots turn yellow, orange or brown, then this gasoline contains resins in high concentrations.

Why does gasoline turn white?
If white spots remain on the glass after the fuel has burned out, this indicates that there are no impurities in the fuel. And if the spots turn yellow, orange or brown, then this gasoline contains resins in high concentrations.

How do you distinguish gasoline from petrol?
How do you recognize petrol?

Odor: Gasoline mixed with gasoline has a pungent odor, not typical of a quality product.
By color: Some drivers said that after looking at the jet's color while adding fuel to the tank, they noticed that "gasoline" was an odd "milky" color.

Which gasoline is better yellow or white?
Good gasoline is usually pale yellow in color and becomes almost colorless in the test tube. ... Aromatic hydrocarbons make gasoline yellow. In other words, if AI-95 gasoline isn't pale yellow, then it's not high quality.

What color of gasoline is best?
Therefore, it is recommended to collect gasoline in a transparent container and look into the light: the fuel should not contain any impurities, and the color should only be light yellow (the exception is network gas stations, where gasoline is colored special Sudan dyes to protect against counterfeiting) .

On this page https://drivrhub.com/what-color-is-gasoline/ you can learn more about gasoline and its properties. I hope this will be useful for you