Actually, it depends. Most machines don't convert. They play 25fps into a 30fps window, and is why you may see ghost streaks. Many machines crop pixels off top and bottom (sometimes just bottom), rather than resizing the palette. The color is output in NTSC values instead of PAL values. The DVD does not have "PAL" or "NTSC" color, but rather the player output DVDs as analog signal, and that's where the color values come from. PAL encoded DVDs often have "hot" or "oversaturated" colors when PAL output is intended, so if you're converting using a disc to disc playing method, you may consider a proc amp in between, to reduce the saturation a tiny bit. Overwise, the new NTSC DVDs may have color bleeding on reds and greens. You may notice this playing PAL on NTSC, and that's one reason I have color modes on my tv (one mode de-saturates).
Just a few things to remember and consider.
Because universal playback quality improves every year, I'm not a fan of converting. Your conversion job this year may look worse than just playing the PAL DVDs as-is in another 1-2 years.