If the flags added in Select aren't transferring to Lightroom or are showing white it's highly likely that you have your Lightroom set up in another language which will block Lightroom from reading the color tags set in Select leading to show white color flags.
You can get this sorted by changing the setting to see the color tags reflected by changing your Lightroom language settings to English or continue with the current language and continue with the steps below:
1. Click on "Metadata" > Click in "Color Label Set" > Click click on "Edit"
2. Type in the numbers of the colors in English
3. Click on "Save Current Settings as a New Preset"
4. Type in "Select" and then click on "Change"
5. Then press ⌘ command + j and to open the view settings. Check that you have the following options marked
After doing this, you should see your color labels as shown below:
Once having done this, the next time you import your images into Lightroom, go to "Metadata" >"Select" and you'll have your reading settings applied