convert srt to son and vobsub
software

srt2sup
subrip
pic2pic
son2vobsub

1.open text srt file with SRT2SUP
set background color to white
set text, outline, antialias color to blue, red or black
(the colors used by DVDMaestro)
other setting just follow this guide

2.select "SRT File"->"Save All as Bitmap"
save as a new srt file and lots of bmp files

3.use pic2pic convert all the bmp files from 32bpp to 16 color format. (don't change the output file names)

4.convert the new srt file to DVDMaestro format (son & spf) with Subrip

5.open *.son file with notepad. change Color and Contrast setting to desired color
(you can modify *.spf as well)

6.convert *.son to vobsub (idx+sub) format with son2vobsub

then it's done.