Describe the bug
When passing a 8 digits HEX color (classic HEX 6-digits + alpha channel), when the alpha channel is 0 the color seems to be ignored and the fallback red color is used.

To Reproduce

1. Pass the following colors={} props to the Heatmap component: ["#6092c000", "#6092c000", "#a8bfda", "#ebeff5", "#ecb385", "#e7664c"]
2. Watch the first 2 buckets get colored in red

Apparently the bug does not appear when using the rgba notation.

Expected behaviour

Transparent color should appear.

Screenshots

Kibana Cross Issues
elastic/kibana#106419