on the black and red wires coming out of a battery?

Red is +'ve

isnt it reversed on a123 cells, black is postive and red is negative?

Not usually. The whole point of using back and red, is so that everyone always knows, red is positive, black is negative. There are no exceptions that I know of.

the cells themselves are not color coded
they are marked with a + sign for positive
and a - sign for negative
there are other ways to identify the pos/neg terminal of a battery also if they are not physically marked

if a company were to mark a positive lead in black and a negative lead in red then they would be leaving themselves open for some serious lawsuits as they would be going against international convention

there are some things in wiring that are just not reversed

like the green wire in house wiring is always the earth ground, red and black are always positive and negative - respectively

It isn't always black and red, it can also be black and white, blue and yellow, orange and black, yellow and black, etc. The colours don't matter, what matters is that the darker wire is always negative.

EDIT: House wiring is AC, there is no positive or negative.

that's true, especially in automotive wiring
but the source power is always red and black, as in from the battery
you don't get into the other colors until power starts to branch

and house wiring is ac and there is no positive and negative per say
but my point was wire colors and how some are constant
green in house wiring is always earth ground
black is always hot and white is neutral