1. light (color, taste, etc.); faint (e.g. smell); pale
その扉が、青く淡い輝きに満ちている。That door is filled with a pale blue radiance.
2. faint (feeling, hope, etc.); fleeting; slight; passing; indistinct (e.g. silhouette)
そういう淡い期待を知らず抱いていたんだろう。They must have been harboring such faint expectations without realizing it.