These are all possible background/foreground combinations possible in DOS:

black on black blue on black green on black cyan on black red on black magenta on black brown on black white on black dark gray on black bright blue on black bright green on black bright cyan on black pink on black bright magenta on black yellow on black bright white on black
black on blue blue on blue green on blue cyan on blue red on blue magenta on blue brown on blue white on blue dark gray on blue bright blue on blue bright green on blue bright cyan on blue pink on blue bright magenta on blue yellow on blue bright white on blue
black on green blue on green green on green cyan on green red on green magenta on green brown on green white on green dark gray on green bright blue on green bright green on green bright cyan on green pink on green bright magenta on green yellow on green bright white on green
black on cyan blue on cyan green on cyan cyan on cyan red on cyan magenta on cyan brown on cyan white on cyan dark gray on cyan bright blue on cyan bright green on cyan bright cyan on cyan pink on cyan bright magenta on cyan yellow on cyan bright white on cyan
black on red blue on red green on red cyan on red red on red magenta on red brown on red white on red dark gray on red bright blue on red bright green on red bright cyan on red pink on red bright magenta on red yellow on red bright white on red
black on magenta blue on magenta green on magenta cyan on magenta red on magenta magenta on magenta brown on magenta white on magenta dark gray on magenta bright blue on magenta bright green on magenta bright cyan on magenta pink on magenta bright magenta on magenta yellow on magenta bright white on magenta
black on brown blue on brown green on brown cyan on brown red on brown magenta on brown brown on brown white on brown dark gray on brown bright blue on brown bright green on brown bright cyan on brown pink on brown bright magenta on brown yellow on brown bright white on brown
black on white blue on white green on white cyan on white red on white magenta on white brown on white white on white dark gray on white bright blue on white bright green on white bright cyan on white pink on white bright magenta on white yellow on white bright white on white

The following combinations were recognized by Opera 9.51 as being OK (i.e., were not substituted with black/white text):

green on black cyan on black magenta on black brown on black white on black dark gray on black bright blue on black bright green on black bright cyan on black pink on black bright magenta on black yellow on black bright white on black
green on blue cyan on blue brown on blue white on blue bright blue on blue bright green on blue bright cyan on blue pink on blue bright magenta on blue yellow on blue bright white on blue
black on green blue on green white on green bright green on green bright cyan on green yellow on green bright white on green
black on cyan blue on cyan bright cyan on cyan yellow on cyan bright white on cyan
brown on red white on red bright green on red bright cyan on red pink on red bright magenta on red yellow on red bright white on red
black on magenta brown on magenta white on magenta bright green on magenta bright cyan on magenta bright magenta on magenta yellow on magenta bright white on magenta
black on brown blue on brown red on brown magenta on brown yellow on brown bright white on brown
black on white blue on white green on white red on white magenta on white dark gray on white bright white on white

The following combinations look really bad and should not be used; Opera 9.51 substitutes with black/white text:

black on black blue on black red on black
black on blue blue on blue red on blue magenta on blue dark gray on blue
green on green cyan on green red on green magenta on green brown on green dark gray on green pink on green bright magenta on green
green on cyan cyan on cyan red on cyan magenta on cyan brown on cyan white on cyan dark gray on cyan bright blue on cyan bright green on cyan pink on cyan bright magenta on cyan
black on red blue on red green on red cyan on red red on red magenta on red dark gray on red bright blue on red
blue on magenta green on magenta cyan on magenta red on magenta magenta on magenta dark gray on magenta bright blue on magenta pink on magenta
green on brown cyan on brown brown on brown white on brown dark gray on brown bright blue on brown bright green on brown bright cyan on brown pink on brown bright magenta on brown
cyan on white brown on white white on white bright blue on white bright green on white bright cyan on white pink on white bright magenta on white yellow on white