Ok, so there seems to be a bit of a rising trend at the moment of characters who were initially conceptualised as being one colour or ethnicity being made a different ethnicity when they are adapted into a different form of media. Here are my thoughts:
Sometimes it's good, sometimes it's bad, sometimes it really doesn't matter. Let me explain:
If a character has been created in a visual medium, e.g. a comic book or an animated TV show, sometimes their appearance is actually a very large part of their identity. Case in point: Jimmy Olsen has always been drawn as and written as a small-built, skinny, kinda dorky freckly ginger (or reddish brown haired) guy who always brings his camera, and isn't always that self-confident but has his heart in the right place.
In the new Supergirl TV series however, he is being played by Mechad Brooks, a muscley 6'4'' black guy who is bald and who in the trailer for the show exudes self-confidence. My main problem here is that what we get simply isn't Jimmy Olsen. Brooks is built to play a badass character like Victor Stone or Black Lightning, either of whom would have worked well in this DC TV Universe, and having seen him in several other TV shows, I honestly think he's a good actor and he'd really suit one of those roles. Je just doesn't have any of the "dorky" or ginger/gingery brown qualities of the real Jimmy.
With that said, where do I stand on the idea of The Doctor in Doctor Who potentially being played by someone of another ethnicity?
I'd be completely fine with it. Go ahead, you can even make the Doctor a woman or give him/her an entirely unusual skin colour if you like.
Why do I think this?
Because it has been very well established in the Doctor Who continuity that Time Lords can regenerate into any skin colour or gender. As the 9th Doctor put it:
"It's a bit dodgy... this process, you never know what you're gonna end up."
Not to mention, even The Master is a woman now!
With that said, I honestly don't feel that James Bond should be played by anyone who isn't white (WAIT BEFORE YOU THROW FOOD AT ME AND ACCUSE ME OF RACISM... PLEASE!), because he was very well described in Ian Fleming's original books physically, and his background with Scottish aristocratic heritage is well established, so casting anyone of another ethnicity wouldn't really match with the history that Ian Fleming had intended, and when you deviate from a character's history in a small way, the chances are that because of that small change you're going to start having to make bigger changes somewhere down the line that continue to draw your character away from his intended origin until eventually you might not have that same character anymore underneath. With that said, if the writers were still able to keep the spirit of the character alive, and if the actor chosen were just really good, maybe I wouldn't mind...
But the problem that we've reached now is that even animated characters are being rebooted as different ethnicities without any real reason, e.g. Brains for some reason being turned from a stuttering white nerd into a not-quite-as-stuttering Indian nerd in Thunderbirds, and it all seems to be [wait, I swear what I'm going to say now isn't intended to be offensive] pandering to political correctness.
There. I said it. Now feel free to throw food at me. It seems that in every team where we had all white characters originally, when a new character is introduced, that character is being made to be one of a different ethnicity to the previous character. With that said, I don't mind this at all, so stop throwing food at me.
Besides, even Benedict Cumberbatch recently said that actors of colour don't get enough roles. What I care about is how well written and how well developed these characters are. That's it.
Or is it?
If we solely cast in a colour-blind manner from now on, we might start to get some problems.
Let me explain:
In several movies and TV series now (e.g. The Adventurer: The Curse of the Midas Box, BBC's Merlin), people of colour have been seen in places or positions which make no sense if a show wishes to be historically accurate. For example, in The Adventurer, twice in the film, a black man is seen as a senior member of the Department of Antiquities, during a time (roughly Victorian times) when sadly he would have been considered more of a second class citizen, and wouldn't have been given such a prominent role.
Now, it seems that in colour-blindly casting someone of this role, we as a people are forgetting how unequal our society has been in the past, and in some ways still is today. If anything, I think we should acknowledge our past societal prejudices, acknowledge that in some areas these prejudices still exist, and do our best to combat racism in casting, while also being sensible in terms of both historical accuracy and in terms of staying true to the original vision of the person or people who created the characters in the first place.