#553 – Setting an Alpha Value in Blend

Colors in WPF consist of 8 bytes–2 bytes each for the alpha, red, green and blue channels.  The alpha channel dictates the transparency/opacity of a color (255 or #FF = fully opaque, 0 = fully transparent).

You can set the alpha value for a color in the color editor in Blend by setting the value of the field labeled A (0-100%) or by explicitly setting the first two bytes of the hex value for the color (#00-#FF).

In the example below, the Alpha value is at 100%, or #FF, indicating that the color is fully opaque.

If you set the Alpha value to 50%, you’ll see that the first two bytes in the color value are now #7F (127).

In the example below, we’ve set the the Foreground color of the label to Black, with an alpha value of 50% so that we can see through the label to the GUI behind it.

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#208 – Color Values Are Stored as RGB Values

Although we can specify colors for brushes in WPF using predefined names, e.g. “DarkBlue”, each color is actually stored as an RGB (Red/Green/Blue) value.

For example, if we specify a color as “Lavender” and then look at the Color property of the SolidColorBrush at runtime, we see that the color is actually a structure containing a number of fields.

The main fields in this structure are the R, G, and B fields, which specify Red, Green and Blue values that make up the resulting color.  Each value has a range from 0-255.  So “Lavender” is: R=230, G=230, B=250.

The A field represents the alpha channel (also 0-255), which dictates that transparency of the object (0 = fully transparent, 255 = fully opaque).

The ScA, ScR, ScG, and ScB properties allowing reading or writing the color in the scRGB format.