That is not true.
Yonex nylon Birdie's color has nothing to do with the speed of the birdie.
Here is a photo from a German site:

And in German:
Mittel = medium in English( as 77 or 5.0g)
Schnell = fast;
Langsam = Slow.
All three speeds have white color and yellow color to choose from.
The cap of the tube does indicate the speed, i.e.:
Green=slow
Red=Fast
Blue=Medium.
I used these birdies when I started to learn, and they are terrible in net shots, and
it is hard to defend when someone smashes at you, it flys like a rock.
And it breaks string easily.
Avoid it if you can.
引用:
以下是引用wei在2003-7-6 23:27:30的发言:
YY的塑料球分三种,适合不同的气候条件,白色的球速快,适合寒冷季节。
总体感觉,打起来比较轻松一些,尤其后场球相对容易,飞行路线平稳。
作为娱乐还是不错的选择。另外,根据规则,在裁判许可的条件下,比赛也可以用塑料球,尽管很少。
一筒6个,大约80元。