complementary

matching

Identical in appearance

• fitProper or healthy
• harmonyAgreement or musical blend
• congruenceState of agreement

compatibility · correspondence · alignment · coordination · counterpart · tandem · interlocking · concordance · unison · dovetailing

opposite

Reverse or contrary thing

• afterimageLingering visual impression
• visualOf or concerning sight
• contrastNotable difference between things

vibrant · red-green · pigment · palette · painting · design · chromatic · hue · tint · shade

mutual

Shared between parties

• give-and-takeMutual concession between parties
• interchangeReciprocal transfer between parties
• exchangeMutual giving and receiving

quid-pro-quo · back-and-forth · symbiotic · cooperative · two-way · interdependent · corresponding · offsetting · correlative · codependent

additional

Beyond the existing amount

• auxiliaryGiving additional support
• supportiveOffering help and reassurance
• ancillaryProviding additional support

secondary · accessory · subsidiary · adjunct · backup · accompanying · extra · add-on · supporting · parallel

geometry

Science of spatial relationships

• right-angleNinety-degree intersection
• perpendicularAt right angles
• trigonometryTriangle angle mathematics

adjacent · acute · math · measurement · degree · supplementary · protractor · vertex · intersection

accentuating

Stressing for emphasis

• amplifyingIncreasing strength or intensity
• boostingIncreasing force or level
• elevatingLifting to higher level

heightening · improving · intensifying · magnifying · enriching · strengthening · augmenting · reinforcing · fortifying · polishing

• color coordinationmatching, palette, scheme, hue, tones
• harmoniouspeaceful, balanced, serene, tranquil, unified
• color theorycolor theory, hue, primary colors, secondary colors, saturation
• angle termsacute, obtuse, right, straight, reflex
• color schemesmonochromatic, analogous, triadic, neutral, warm colors
• Dualityduality, dual nature, two sides, yin and yang, yin-yang