alpha:
Cx phrases for x values:
results are out of 255
0-0
1-8
2-16
3-24?
4-33
5-41
6-49
7-57?
8-66?
9-74?
a-82?
b-90?
c-99?
d-107?
e-115?
f-123

Dx phrases for x values:
results out of 255
0-132
1-140
2-148
3-156
4-165
5-173
6-181
7-189
8-198
9-206
a-214
b-222
c-231
d-239
e-247
f-255

DF for different reds (the reason this is here is that for reds above 7F, it acts strangely. I don't think any reds that high occur in the game ever.)
results out of 255
00-0
10-33
20-66
30-99
40-132
50-165
60-198
70-231
80-0
90-33
a0-66
b0-99
c0-132
d0-165
e0-198
f0-231





colour (see notes at bottom! They're important!):
first digit:
adjust Red (notice how going above 7 acts strangely!):
0-0
1-33
2-66
3-99
4-132
5-165
6-198
7-231
8-231
9-165
a-198
b-231
c-0
d-33
e-66
f-99


second digit:
adjust Green:
0-0
1-66
2-132
3-198
4-0
5-66
6-132
7-198
8-0
9-66
a-132
b-198
c-0
d-66
e-132
f-198

adjust Red:
0-0
1-0
2-0
3-0
4-8
5-8
6-8
7-8
8-16
9-16
a-16
b-16
c-24
d-24
e-24
f-24


third digit:
adjust Blue:
0-0
1-132
2-0
3-132
4-0
5-132
6-0
7-132
8-0
9-132
a-0
b-132
c-0
d-132
e-0
f-132

adjust Green:
0-0
1-0
2-8
3-8
4-16
5-16
6-24
7-24
8-33
9-33
a-41
b-41
c-49
d-49
e-57
f-57



final digit:
adjust blue:
0-0
1-8
2-16
3-24
4-33
5-41
6-49
7-57
8-66
9-74
a-82
b-90
c-99
d-107
e-115
f-123

Screenshots may produce differing results, because of the way hardware determines how to display colours in 16-bit colour mode. I have not determined the internal values used by LR2 for certain, but I believe they would produce the same range of values for each channel, whereas on my machine, red and blue have the same range, and green never reaches 255. I had some time to test another computer, and it had the same red and blue values as my main machine gives, but very slightly higher green values. I believe the current tables are accurate to LR2's internal values.
To recreate the sprites more faithfully, you need to put them in a 16-bit colour environment and do calculations in there. These tables should give you all the right values, but! Using higher precision with alpha means that you'll get different results when putting sprites on top of each other than the results the game has.