For a slightly softer look (less eye strain), use 80% gray (#CCCCCC) instead of pure white. You still get full visibility without the "washed out" look.
You're looking for information on the Fullbright 1122 resource pack! fullbright 1122 resource pack full
: Removes shadows and darkness, allowing you to see clearly in caves and underwater as if it were broad daylight. Dimension-Wide Support For a slightly softer look (less eye strain),