远处有些小山,也是灰色的,比天空更深一些;因为不是没有阳光,小山上是灰里带着些淡红,好像野鸽脖子上的彩闪。
猫城记,老舍, p.7 (photo; alt)
I'd translate this to:
In the distance there are some small mountains, which are also gray, darker than the sky; 因为不是没有阳光, the grayness on small mountains brings with it some redness, like the glistening of a wild dove's neck.
It feels like the double negative used in 因为不是没有阳光 is intended to say something like "because there's still a wee bit of sun", equivalent to something like 还略有阳光. I'm unclear on this point.
Question: Why does 老舍 in《猫城记》 use the phrase 不是没有 in 因为不是没有阳光?