Yes, it is. You can also say Tương lai xám xịt (or ảm đạm) của tôi. They sound more natural.
From Chinese 將來
- Mandarin: jiānglái
- Cantonese: jēunglòih
- Hokkien: tsiong-lâi
TranVanHaiNam answered it above. If you said "Tương lai của tôi xám xịt" or "Tương lai của tôi ảm đạm", then it's the equivalence of "My future is gray."
In other words, 'màu xám' means that my future is the colour grey, which is incoherent, and doesn't have the same metaphorical meaning as a grey future does in English?