What does "on his dignity with" mean in "The Case of the White Footprints"?

Question

In "The Case of the White Footprints" in Dr. Thorndyke's Case-Book by R. Austin Freeman, a woman was talking to a detective about a situation in her hotel, saying:

Mr. Bergson wasn't drunk, but he was excitable and noisy, and when I told him he mustn't come again he made such a disturbance that two of the gentlemen boarders—Mr. Wardale and Mr. Macauley—had to interfere. And then he was most insulting to them, especially to Mr. Macauley, who is a coloured gentleman; called him a "buck nigger" and all sorts of offensive names".

"And how did the coloured gentleman take it?"

"Not very well, I am sorry to say, considering that he is a gentleman—a law student with chambers in the Temple. In fact, his language was so objectionable that Mr. Wardale insisted on my giving him notice on the spot. But I managed to get him taken in next door but one; you see, Mr. Wardale had been a Commissioner at, Sierra Leone—it was through him that Mr. Toussaint got his appointment—so I suppose he was rather on his dignity with coloured people."

I think that the bolded "he" refers to the coloured man, but the bolded "his & him" refer to "Mr. Bergson"? As it is illogical that Mr. Wardale wanted her to dismiss the coloured man!! Is that right?!

And does "on his dignity with coloured people" mean "he think that coloured people must be respected" or "he treated their dignity as if it was his own"?

Answer 1

To be on your dignity is to act in a very formal manner, in order to

to demand to be shown the respect that you think you deserve:

So, Mr. Wardale is being demanding because Mr. Macauley's language is so objectionable (despite the provocation) that it shows too much disrespect. (Into the logic of that we shall not delve.)

As a Commissioner, being on his dignity was necessary to keep his work going, so he got into the habit and expects it even here.