Update doc/python/supported-colors.md

Author: LiamConnors

doc/python/supported-colors.md

@@ -53,7 +53,7 @@ fig = go.Figure([
 fig.show()
 ```
 
-These colors are supported in Plotly.py when a property accepts a [named CSS colors](https://developer.mozilla.org/en-US/docs/Web/CSS/named-color).
+These colors are supported in Plotly.py when a property accepts a [named CSS color](https://developer.mozilla.org/en-US/docs/Web/CSS/named-color).
 
 ```python hide_code=true
 import plotly.graph_objects as go