AK-74s use a different colored magazine. They are reddish brown not black. There are no exceptions to this as far as I know. The color coding was probably done intentionally so that the two are not confused in the field.
Since these weapons are now pretty common in the US, I would guess 5-10% of the population know of this off hand, and would easily be able to identify it as either AK-74 type weapon from several hundred yards. Either that or someone not knowing jack did notice the funny colored box protruding from the under side of the weapon.
Black mags are available for AK-74. K-VAR has them. They are smooth-sided, as opposed to ribbed (metal) or waffle (plastic) as the AK-47s are. This done to help ID at night. And red bakelite can be "cooked" to change color.