Streak color is the color of the finely-pulverized mineral. Streak plates are snow-white, unglazed ceramic tiles. You can use the back of a white, glazed tile from the hardware store to rub the mineral sample to produce a streak.
This only works for minerals which are softer than a ceramic tile (hardness ~ 7).
Example Subject Searches
Example: "streak-red*" finds all minerals with a red or reddish sreak.
Example: "streak-reddish-brown" finds all minerals with a reddish brown streak.