All you have to do is to declare them for each cell. That made no sense, so here's an example:

print Tr(
    {-align=>'center',-valign=>'top',-bgcolor=>$trBgColor},
    [
        th( { -style => "background: #ffffff" }, "Column1" ),
        th( { -style => "background: #cccccc" }, "Column2" ),
        th( { -style => "background: #ffffff" }, "Column3" ),
    ]
);
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