What would the difference be in Polish between "purpurowy" and "fioletowy"? Judging by image searches, I would say they're closer to "purple" and "violet" respectively. Or would a Polish person not differentiate between the two?
"Fioletowy" is definitely more general, common and casual: when teaching a child colors you would teach them "fioletowy" (meaning the all the colors that come up when you google it;)).
A Polish dictionary defines "purpurowy" (adj.) as "a dark red with a shade of violet" (see http://sjp.pwn.pl/szukaj/purpurowy.html). There is a word "purpurat" meaning a cardinal in the Roman Catholic Church (nowadays; before: a man wearing a robe in the "purpurowy" color denoting his high rank). According to the dictionary http://sjp.pwn.pl/szukaj/purpura.html the name of this color, i.e. "purpura" (n.), can refer to "dark red with a shade of violet", "a dress in this color, especially a regal coat or a robe of a cardinal", "a natural dye color ranging from scarlet (Pol. "szkarłatny") to violet (Pol. "fioletowy")" (you can compare this with http://www.thefreedictionary.com/purple). Another dictionary (Brueckner, 1927) claims that "pupurowy" is the same as "szkarłatny". And with "szkarłatny" in my opinion everything is clear: it is a special kind of dark red (see http://sjp.pwn.pl/szukaj/szkar%C5%82at.html), that kind which you would see on a kings coat or the color of blood (https://pl.wikipedia.org/wiki/Szkar%C5%82at). But on the other hand, in some English sources the color "scarlet" is defined as "strong to vivid red or reddish orange" (http://www.thefreedictionary.com/scarlet, cf. the English Wikipedia)...
Therefore, I would say:
- "purpurowy" has a more noble feeling to it and you should treat it as special kind of "fioletowy" or even "czerwony",
- similar names can designate slightly different colors in different languages (and probably the meaning of "purpurowy" is shifting due to the influence of English).
Bare also in mind that the Internet is probably not the best place to display and depict colors (due to the calibration of different monitors)...
Also, for further reading about "fioletowy" and its names in the past, see http://sjp.pwn.pl/poradnia/haslo/Jak-dawniej-nazywano-kolor-fioletowy;15064.html (unfortunately only in Polish).
Well. OK. There is a list of colours on Polish Wikipedia, it lacks sources and I do not know where those names and values are used (in publishing possibly), so I have no idea how much and where is it reliable… but have fun. ;-)
EDIT: Yeah, I checked and the list claims that purpurowy is red (czerwony) mixed with fioletowy (violet). So that is at least one difference present for at least some natives.