It could be a misinterpretation of inaccessible, but as colleague Felipe Lorenzo del Río says it is surely a mistake because it was unfading, which was already defined with its own entry.
Corrected inmarcesible, from Latin: in- , prefix privativo and marcesco , wither , ajarse , languish . That it cannot wither, eternal, imperishable, perennial, immortal. It is a term of literary use that people do not usually use.