You are comparing skin colour with sexual orientation, which is fine, to an extent.
To what extent is it not?
You can certainly compare barring one black person from your hotel with barring one gay person on his own.
If that was what was happening, yes.
I'm not sure you can compare barring a gay couple from a double bedroom (provided they are offered single rooms) with barring a black straight couple.
Of course you can if a gay couple are being prohibited from service because they are gay (which is their nature, it's not something like a religion or a political affiliation which they've chosen) then you can compare it fairly clearly with prohibiting a black couple from service because they are black (which is their nature, it's something like a religion or a political affiliation which they've chosen).
If you were barring a Muslim because they're a Muslim then although it's equally protected under the law, it's not a directly comparable situation.
In that case you would be preventing a specific activity that you believe is wrong.
There are people who believe that 'being' black makes you somehow lesser, less deserving. I believe that being a Christian fundamentalist is idiocy of the first order, to a level that's verging on offensive in a first world country, but that doesn't give me the right to refuse service because someone's a Young Earth Creationist.
I know the activity is legal, but I don't think one can compare skin colour with an activity.
And if a mixed race couple were to try to book a room and be turned away...? There are people who believe that 'activity' is wrong, do they have grounds to refuse service? And if so, is it any different to refusing a gay couple?
You might bar more than three children from a sweet shop at once, to prevent disruption, but you wouldn't bar children in general.
The children aren't banned, though, the situation in which they are permitted to do everything anyone else can do is moderated; and it's done so in order to achieve the specific, demonstrable, justifiable aim of reducing shoplifting. Discrimination is permissible where it can be shown to be justified.
O.