If you want to see red leaf in Hong Kong. You can go to a place call "Tai Tong 大棠". It is located in Yuen Long. You can take the railway to Yuen Long Station then take a taxi or van to get there.
http://maps.google.com.hk/maps?f=q&source=s_q&hl=zh-TW&geocode=&q=%E5%A4%A7%E6%A3%A0&brcurrent=3,0x3403fa3d793f3dd1:0x259ffe38cb9f823c,1,0x3403f00a63639461:0xba0588d41c361655&brv=22.25&sll=22.416645,114.016725&sspn=0.001136,0.002642&ie=UTF8&hq=&hnear=%E5%A4%A7%E6%A3%A0&z=13
The pictures below was taken at the end of November on last year.