I just released AnsiColor 0.2.0 that now supports the ANSI conceal code. Conceal code 0x8 is a hacky way to hide data inside text using ANSI sequences. Jenkins uses it to annotate output with something that looks like ha:<long base64 string>. You can see this implemented in ConsoleNote.java. The previous version of AnsiColor produced garbage by stripping the conceal sequence, therefore revealing the content inside the conceal block (issue #3). Fixed in this commit. Also updated Jansi to 1.7 – Jansi makes this plugin possible.
Update your Jenkins.