If I understand the article correctly, the material can be designed to absorb, rather than reflect, certain frequencies of electromagnetic radiation. When this occurs in the visible spectrum, we call such materials, "black". If it were really effective, clothing made from it would appear to be so dark that it couldn't get any more black--aka none more black. Existing clothing might not be quite that dark but it probably gets pretty close in terms of human visibility.
The article would probably be more accurate to call this advancement a potential improvement to stealth technology since it sounds like the intent is to conceal planes from radar.