Well, I have a context from personal experience that crosses two speech community boundaries that I now recognise, for the sunshine component at least. The term was in fairly common use in a jokey way by us kids in Kent and Sarf Lunnen - "oi, sunshine, whatcher doin' ternight?" Then, when I was going to a gig at the Hammersmith Empire (Dr Hook & the Medicine Men, great gig fwiw) we got stuck in a queue of people without tickets, despite already having tickets ourselves, which was being held back by a big black bouncer on the door. We all tried to get his attention to explain, to no avail. At one point, entirely unconsciously I called out that phrase which amongst our group was a badge of matey solidarity - "Hey, Sunshine, we've GOT tickets...!"

The whole crowd in front of us went silent. He stopped chatting up the girl at the front of the queue and swung around with a look that could kill at ten paces. Putting on his best Jamaican accent he enquired who wanted to talk to him... I 'fessed it was me, with a nervous grin suddenly realising how small and pale I must be against this giant as he came through the crowd. What a nice day to die! I guess he could see from my demeanor that there was no threat or challenge involved, which made him just reconsider for a moment. Then he asked me if we'd driven up to the gig - "well, you prob'ly heard we just love love you' white cars in Brixton, mahn!" as the previous week there had been major riots in that district. When our gang and the crowd around us laughed with him, the tension drained away, and we got talking.

Point is, I was left in no doubt at all that 'sunshine' meant one thing to a white kid using London patois and quite a different thing to a black kid using West Indies patois. I assume the slur element is taken from racists having insulted darker-skinned people about having been out in the sun too long and all that sort of offensive crap. I'll be interested to hear if anyone has anything that corresponds to elements of this, or adds anything about the 'Mr' part of the original question. Does that have specific connotations?