I have "network-workgroup" in the icons.toml file and use it in code:

gtk::Image {
    set_icon_name: Some(icon_names::NETWORK_WORKGROUP),
},

the generated file icon_names.rs contains these lines:

/// Icon name of the icon `network-workgroup`, found at `"icons/icon-development-kit/network-workgroup-symbolic.svg"`.
pub const NETWORK_WORKGROUP: &str = "network-workgroup";

the problem is the icon shown is not network-workgroup-symbolic but simple network-workgroup with colors.
If I set_icon_name: Some("network-workgroup-symbolic") I get a symbolic icon as expected.