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I know I can take a color and multiply it by a float to reduce its alpha like that:

Color color = Color.Green * 0.15f;

But how do I return the color's alpha to it's original value?

I tried doing this:

color.A = 255;

But it seems like I get a different color. (The RGB are different then those of the original color).

Also, just changing the alpha of the original color (directly, not by multiplying) doesn't make it transparent..

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    \$\begingroup\$ Divide by the same amount. \$\endgroup\$ – Vaughan Hilts Aug 14 '13 at 13:47
  • \$\begingroup\$ It isn't possible to divide for some reason.. \$\endgroup\$ – Ofir Aug 14 '13 at 14:18
  • \$\begingroup\$ @Ofir See how msdn.microsoft.com/en-us/library/… has an op_Multiply function? This is why color * float works. There is no op_Division but this should work color = color * (1 / .15). \$\endgroup\$ – ClassicThunder Aug 14 '13 at 14:32
  • \$\begingroup\$ How silly - but yes, just use inverted mulitplication. Thanks @ClassicThunder \$\endgroup\$ – Vaughan Hilts Aug 14 '13 at 14:38
  • \$\begingroup\$ It works but It's not 100% accurate. Thanks anyway, I'll just do it in another way. \$\endgroup\$ – Ofir Aug 14 '13 at 14:41
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You are multiplying all color components, not only the alpha channel (Color.Green * 0.15f;) To only change the alpha:

Color color = Color.Green;
color.A *= 0.15f;
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  • \$\begingroup\$ This is wrong because it is not taking into account the fact that he is using XNA and thus premultiplied alpha. \$\endgroup\$ – ClassicThunder Aug 14 '13 at 12:28
  • \$\begingroup\$ Like I wrote in my post, directly changing the alpha doesn't make the object transparent. \$\endgroup\$ – Ofir Aug 14 '13 at 12:40
  • \$\begingroup\$ -1 because Xna uses premultiplied alpha \$\endgroup\$ – Blau Aug 14 '13 at 13:57

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