In Clover HTML reports, test coverage is indicated by the following colour-coded legend (also available on each source page via the 'SHOW HELP' link in the header on each page):

The page margin has three colour indicators:

• left half with line number is the "optimistic marker", which is highlighted in:
  
  • green when at least part of the code line was covered during execution
  • otherwise red if it was not covered at all
• right half with number of hit counts (i.e. how many times given line was executed) is the "pessimistic marker" which is highlighted in 
  • red if at least part of line was not executed or when branch expression was not evaluated to both true and false
  • otherwise green if the whole line was fully covered
• narrow strip related with per-test code coverage, which is:
  • dark green if given source line was executed at least once from a successful test case (i.e. test has passed), or
  • dark yellow if given source line was executed from one or more test cases, but all tests were failed or
  • empty if given code was not executed from a test case (for instance from "main()" method or called by JVM GC "finalize()" method)