Possible Clues:

• Bright side
• Upside of 9-Across/65-Across ... and, chemically speaking, what each pair of circles represents
• What every cloud has
• Positive spin on a bad situation, or a feature of 20-, 31-, 38-, and 45-Across
• Redeeming feature of change by Heather around home
• Upside, when down
• Bright side of an unfortunate situation
• Redeeming aspect of an unfortunate situation
• Sign of hope amid the gloom
• Consoling aspect of a difficult situation