Another vote here for screw-in filters.
I'm not sure what you mean about adding magenta to your shots. If you're talking about color corrections that you're performing digitally, I'd keep that step there and not try to do it with a filter. You'll have a lot more control there.
A good, simple start with filters would be:
UV - cuts haze and protects the lens. Use this all the time when you're not using other filters.
Yellow - adds contrast to B&W and makes the grey tones seem more natural to the eye. Many B&W shooters use a yellow filter the way color shooters use a UV: they never take it off unless they're using another filter.
Polarizer - I won't get into how it works, technically, but the effect is increased contrast and color saturation and a reduction of glare and specular highlights. It takes a little figuring at first, but they can really add a lot to outdoor shooting.
A good, simple second round might include:
1A "skylight" - similar to a UV filter, but it warms up color tones just a bit. It has no significant effect upon B&W, so it's interchangeable with a UV in that application.
Orange - for even more contrast and dramatic skies in B&W.
Red - even MORE contrast and dramatic skies!
ND - enable you to shoot with wider apertures when your film (or sensor) is too fast. I haven't played with these much, so I'm not much of an authority on them.
That's likely all you'll ever need 90% of the time. Sometimes B&W shooters will use green or blue for special effects and studio photographers still using film may use color correction filters for certain types of lighting but the one's I listed above will get you through most situations. When I was shooting more color I used a polarizer quite a bit. Now I mostly shoot B&W and find that I seldom use anything other than yellow or orange. Sometimes I use special infrared filters, but that's an exception.
Have fun experimenting!