Apparently Topaz is a gemstone, just as you have found on google. The color is not independent, meaning that it can be a variety of colors. I have, however, mostly seen it is a deep blue - bluish green - color.
Here is an excerpt from a website I'll give you a link too:
Color: Pure topaz is colorless, but it also occurs in a broad range of colors: yellow, blue, pink, peach, gold, green, red, and brown. Some natural yellow stones are heated to become permanently pink (pinked topaz).
Encyclopedia of Gemstones - Topaz. Topaz's color, characteristics of Topaz, varieties of Topaz, mystical power of Topaz, healing ability of Topaz, Topaz's history
So yea, it's a gemstone. I think the color your friend was referring to was bluish green.
