When, in ordinary life, we speak of the colour of the table, we only
mean the sort of colour which it will seem to have to a normal
spectator from an ordinary point of view under usual conditions of
light. But the other colours which appear under other conditions have
just as good a right to be considered real; and therefore, to avoid
favouritism, we are compelled to deny that, in itself, the table has
any one particular colour.
[Problems of philosophy, Bertrand Russell, Chapter I]
one meaning of "right" as a noun is "a moral or legal entitlement to have or do something."
So Russell is saying (somewhat figuratively) this. If the table appears to have different colors under different conditions, it is not proper to attribute one color to the table. Any of the possible colors is equally valid. (I happen to believe that this is nonsense, but it is what is meant.)
It is somewhat figurative because we normally do not think of colors as having moral or legal entitlements.
Perhaps you are puzzled by the adjectival phrase just as good? I'll paraphrase: "These other colours have a right to be considered real, and their right is exactly as valid as the first colour's right."