Color negatives developed by the C-41 process no longer contain silver. As the silver is developed, dye-coupling reactions activate the color dyes that make the final image. The bleach/fix stage then removes all of the silver. "Fix" means a chemical that will remove undeveloped silver, which is done for conventional B&W negatives. "Bleach" means a chemical that will remove developed silver. Since no silver is left, there is no silver for the selenium to react with and selenium won't intensify the negative.(posted 8449 days ago)If you want higher contrast, you could try a higher contrast paper. If your negatives are underexposed, perhaps some copy negative process would help a little. For color, some of these adjustments are easier by scanning and then making adjustments in the digital realm.