Differences...
Those that have heard all this before please bear with me...The textbook definition of heroin is as a white, odorless, crystalline powder. The majority of the world's users do not have access to pharm. grade product though and have to make do with illicit supplies.This is where the confusion [for some] comes in. Most illicit heroin is classified as two grades: #3 and #4. #3 is manufactured for amoking and is made in Sw and SE Asia. It usually is admixed with caffeine and other substances at the point of distribution. The caffeine is to make it suitable for smoking as it has a lower melting point than heroin, allowing less heroin to degrade under heat. In addition, in #3 from SE Asia, you will usually find strychnine in small percentages as a flavoring agent, as well as quinine and often a sedative to potentiate the experience [most often Barbitone]. This heroin is brown to grey if it comes from SE Asia but brown if it comes from SW Asia as they do not normally add any sedatives that would cause a lighter color.
#4 is produced in SE Asia and is white in color, close in appearance to pharm. grade. This heroin is used primarily for injection but can be insufflated as well. It cannot be smoked effectively though.
Columbian heroin [the majority of powder heroin in the US] is brown to snow white but is not officially classified as either #3 or #4. Even if brown, it is made for injectionor insufflation, not smoking.
Lastly, in the world of illicit heroin there is "Tar." this is produced only in Mexico and is relly only found in the southern and western halves of the US. This owes its distinctive appearance to its producers omitting 2 of the major steps in the heroin production scheme. They take processed opium and directly acetylate it...thus making heroin without first making morphine [as other producers do].
All forms of illicit heroin can be adulterated and tar is always impure due to its poor synthesis. People sometimes feel that tar is superior due to its distinctive appearance [gummy] rendering it resistant to adulteration or dilution. That is a false notion. You can adulterate it in a number of ways. most are admittedly crude and easy to detect [coffee, mollasses, prunes] but it can also be heavily diluted with lactose by converting the tar to liquid admixing carmelized lactose and reconstituting the new mixture, the user never the wiser.
In strictly chemist's terms, brown is always less pure than white because the brown coloring is due to colred impurities that can be easily removed via activated charcoal or other means. Still, one can find brown or white that are purer than each other...it comes down to a crap shoot.