I have SP 2019 on-prem environment. Created the subsite using Communication Template (As of now I was unable to create the Subsite using Communication Template so I found some trick to create it - Reference URL).
Then I applied the Orange theme on a Site collection, Blue color on Subsites.
The problem was when I visit the root site collection, then the subsite theme color was changing to Orange. This is happened only after visiting the Root site collection (Orange theme).
Also, I have checked with Default Team site template same problem occurs
Anyone experienced with this type of Problem or Can anyone suggest any solution for this issue.