Understanding colors on Android (six characters)

Thiago picture Thiago · Mar 26, 2011 · Viewed 158.6k times · Source

I am trying to understand how colors work in Android. I have this color set as the background of my LinearLayout, and I get a background gray with some transparency:

<gradient android:startColor="#b4555555" android:endColor="#b4555555"
 android:angle="270.0" />

If I remove the last two characters (55) I get a solid color, losing the transparency. I was trying to find a page where I can see some explanation about this, but I couldn't find it.

Answer

BlondeFurious picture BlondeFurious · Jun 13, 2012

Android uses hexadecimal ARGB values, which are formatted as #AARRGGBB. That first pair of letters, the AA, represent the alpha channel. You must convert your decimal opacity values to a hexadecimal value. Here are the steps:

Alpha Hex Value Process

  1. Take your opacity as a decimal value and multiply it by 255. So, if you have a block that is 50% opaque the decimal value would be .5. For example: .5 x 255 = 127.5
  2. The fraction won't convert to hexadecimal, so you must round your number up or down to the nearest whole number. For example: 127.5 rounds up to 128; 55.25 rounds down to 55.
  3. Enter your decimal value in a decimal-to-hexadecimal converter, like http://www.binaryhexconverter.com/decimal-to-hex-converter, and convert your values.
  4. If you only get back a single value, prefix it with a zero. For example, if you're trying to get 5% opacity and you're going through this process, you'll end up with the hexadecimal value of D. Add a zero in front of it so it appears as 0D.

That's how you find the alpha channel value. I've taken the liberty to put together a list of values for you. Enjoy!

Hex Opacity Values

  • 100% — FF
  • 95% — F2
  • 90% — E6
  • 85% — D9
  • 80% — CC
  • 75% — BF
  • 70% — B3
  • 65% — A6
  • 60% — 99
  • 55% — 8C
  • 50% — 80
  • 45% — 73
  • 40% — 66
  • 35% — 59
  • 30% — 4D
  • 25% — 40
  • 20% — 33
  • 15% — 26
  • 10% — 1A
  • 5% — 0D
  • 0% — 00