Hugo color theme not changing [params.palette]

I want to switch the theme color to blue, red or yellow, but it just doesn't work. the default is green color theme.

[params.palette]
    primary = "red" //I do change this to blue, yellow or green.
    accent  = "teal"

https://github.com/digitalcraftsman/hugo-material-docs/blob/master/exampleSite/config.toml

what could be the issue?