If you can't see the difference then...
... it's unlikely they'll understand even when the difference is laid out in detail. Still, there's always a small chance.
Two important concepts here are 'sexual disgust' & 'innate racial aversion' (as opposed to racism based on stereotypes).
Sexual disgust is something that stops folk wanting sex with all but the fittest of partners. It's affects women much more than men, which makes sense per the biological differences, e.g. female anatomy being more vulnerable to STDs , etc. Different women have different levels of sexual disgust - those who work as whores long term will often have much less than average. Still, some WG's will still have a close to average level of disgust, these are the ones who have to mostly fake their enjoyment with us unattractive middle aged men.
'Innate racial aversion' is something that the vast majority of the world's population seem to have. There's been studies finding that even toddlers have a preference to play with others of their own ethnicity - and that this preference is stronger than their desire to play with others of the same gender & social class.
Granted there's a sizeable minority who don't have any aversion for other ethnicities - people also have an innate tendency to seek out diversity, in some individuals this counter balancing tendency is the stronger.
And even for those with a strong innate aversion, it doesn't have that big an impact on normal social interactions. (Unlike despicable unchallenged racial stereotypes.) E.g. , even two people of different colours & maxed out innate racial aversions could easily become platonic friends if they were otherwise compatible. Yet when it comes to that most intimate of relations, an above average innate aversion can make the act quite unthinkable for a lass who isn't lucky enough to have low levels of sexual disgust.
I don't know for sure, but I'd guess the above is the most common reason for ethnic refusals - sometimes concerns about dick size or bad experiences will be white lies. Of course sometimes they are not, e.g. sometimes ethnic women will refuse to see their own ethnicity.
PS - just in case the above is disheartening to any non white punters, it is also the case that:
* Some white women actually prefer black or brown skinned men.
* Most other WGs dont mind either way, any very slight ethnic aversion they might have is much less than the aversion they have to unattractive, old, overweight punters of their own race, and easily overcame by the inducement of a punters hard earned cash.
