Is every yellow discharge considered a “ṣufrah,” or can it be among the pure discharges, and does that depend on the degree of yellowness?

As long as you are not certain that the discharge is impure, you are not required to tie a cloth [to prevent it from spreading]; because the rule is that something does not become impure through doubt. It appears that this white discharge is not a yellowish one. It is recommended to completely disregard these [types of] whisperings and not pay attention to them.