00是完全透明(百分百透明)，FF就是完全不透明
透明度 16进制表示
0% FF
1% FC
2% FA
3% F7
4% F5
5% F2
6% F0
7% ED
8% EB
9% E8
10% E6
11% E3
12% E0
13% DE
14% DB
15% D9
16% D6
17% D4
18% D1
19% CF
20% CC
21% C9
22% C7
23% C4
24% C2
25% BF
26% BD
27% BA
28% B8
29% B5
30% B3
31% B0
32% AD
33% AB
34% A8
35% A6
36% A3
37% A1
38% 9E
39% 9C
40% 99
41% 96
42% 94
43% 91
44% 8F
45% 8C
46% 8A
47% 87
48% 85
49% 82
50% 80
51% 7D
52% 7A
53% 78
54% 75
55% 73
56% 70
57% 6E
58% 6B
59% 69
60% 66
61% 63
62% 61
63% 5E
64% 5C
65% 59
66% 57
67% 54
68% 52
69% 4F
70% 4D
71% 4A
72% 47
73% 45
74% 42
75% 40
76% 3D
77% 3B
78% 38
79% 36
80% 33
81% 30
82% 2E
83% 2B
84% 29
85% 26
86% 24
87% 21
88% 1E
89% 1C
90% 1A
91% 17
92% 14
93% 12
94% 0F
95% 0D
96% 0A
97% 07
98% 05
99% 03
100% 00