The source code includes a folder called "_colors" if you downloaded SCSS files. Definitions of colors are in the folder. You may compose them and modify the colors.
but I thought the ''light theme pro' schema is pre-defined...
<link href="_content/Volo.Abp.AspNetCore.Components.Web.LeptonTheme/styles/lepton6.css" rel="stylesheet" id=LeptonStyle /> I tried to switch the css file, but not work.