Initializing color in gl space without alpha gives unexpected results

[pohlt]

Observations:

• No alpha value for gl seems to be fine: chroma(0.5, 0.5, 0.8, "gl") = #8080cc (expected)
• Until you use this object: chroma(0.5, 0.5, 0.8, "gl").brighten(1) = 1 (unexpected)
• Adding an alpha value helps: chroma(0.5, 0.5, 0.8, 1, "gl").brighten(1) = #b1afff (expected)