Both of these colors are muted violet reds. Naphthamide Maroon (PR171) is slightly more reddish while Perylene Violet (PV29) is slightly more violet, though they’re nearly indistinguishable.
Pigment Properties
Lightfastness
Daniel Smith gives both of these colors “excellent”; Bruce MacEvoy suggests Perylene Violet may be LF2, while Naphthamide Maroon by all indications is LF1.
Toxicity
Both pigments are nontoxic.
Price
Naphthamide Maroon is cheaper; DS includes it in their series 1 (cheapest) paints, while Perylene Violet is series 3. As of this writing, a 15ml tube of Naphthamide Maroon costs me $11.18 at Blick, while a 15ml tube of Perylene Violet costs me $14.97. But Naphthamide Maroon only comes in 15ml, while Perylene Violet also comes in 5ml, so it’s easier to test.
Color Mixes
Hansa Yellow Deep (PY65)
Dark, muted coral reds. As you might expect, the maroon mixes are a bit brighter and warmer than the violet mixes. I find the gray-brown in the middle of the Perylene Violet mix to be quite ugly, but I could see dropping Naphthamide Maroon into, say, a sunset.
Phthalo Turquoise (PB16)
Phthalo Turquoise seems to neutralize the Naphthamide Maroon slightly more than the Perylene Violet, while the Violet results in more violet-ish shades. Again the maroon seems to mix a bit redder than the violet.
Perylene Green (PBk31)
Both these colors make dark neutral blacks. In these examples, I was able to achieve darker blacks from Perylene Violet, but in both cases I found it difficult to predict the darkness of the mixes when dry due to the drying shift of all three of these pigments.
Conclusion
Both in unmixed hue and color mixes, these colors are extremely similar, with the Naphthamide Maroon being slightly redder and the Perylene Violet being slightly more violet. Both colors have a fairly annoying level of drying shift.
The use case I find most useful for Perylene Violet is making dark reds, e.g. the shadows of a red object. Naphthamide Maroon does this just as well.
I like the Maroon better in warm mixes; it doesn’t seem to dull things as much. I feel like I’m often disappointed by the way Perylene Violet mixes, and Naphthamide Maroon is just different enough to push it over the line to interesting to me.
In cool mixes, Perylene Violet is more prone to make dull violets while Naphthamide Maroon is more prone to neutralize the cool shades. Personally, again, I find Naphthamide Maroon a bit more useful here, since I have plenty of ways of making dull violets but sometimes find it difficult to neutralize blues. The relative usefulness of these applications will depend on the other colors in your palette.
My Pick: I feel silly even having a preference since these are so similar, but I have to say I like the Naphthamide Maroon better. This is handy, since it’s also the (possibly) more lightfast and (definitely) cheaper one.