I wonder if some sprite masking with a white outline would look good and be fast enough?

Well, the sprites are all made with a Tool that was coded by Spellshaper (he was an omnimaga member, too - or is he even still member?) and me:

Draw 'n Map

I wonder if some sprite masking with a white outline would look good and be fast enough?

Hmmm, I tried it several times but (using xLIB) that would actually cause a major slowdown 

That brings me to another idea... If tr1p' was still around, do you think we could make him implement a greyscale tilemap engine? 
He could maybe add some optional parameters including the second tileset and stuff?

Just an idea...

p.s.
yes, I am advertising  

Do you know why it happens?

Well, it's quite simple: two commands calling two different pictures [overwrite, then match the second with the first in order to 'greyscale' it] instead of one single, sexy line.
Secondly, if you want to make it scrollable, you'll have to redraw the tilemap twice [and then maybe save it in two picture vars in order to speed the greyscale engine up]

xLIB is a great amplification to TI-Basic - but it's still not 'perfect'.

No, it is b/w. I was talking about how it behaved when I tried to make it greyscale...

I don't know much about sprites and such but would it not be possible to make the character sprite one with a white border around it? Like just one sprite with that instead of two separate ones.

Yes, i know what you are talking about - a mask. When I was coding this 'engine', I tested methods like this but it turned out that I was not able to establish a greyscale engine that actually runs smooth.
It's just like the 3D-Problem with xLIB - it is too slow since TI-basic is being interpreted by the O.S.