Lack of light

blackness, shadow, dimness; see darkness 1.

A degree of color

cast, tone, hue; see color 1, tint.

A slight difference

variation, proposal, hint; see suggestion 1.

An obstruction to light

covering, blind, screen; see curtain.

A ghost

spirit, manes, revenant; see ghost 1, 2. See syn. study at color.

To intercept direct rays

screen, shelter, shadow, cast a shadow over, overshadow, eclipse.

To make darker

darken, blacken, obscure, cloud, shadow, make dim, adumbrate, tone down, nigrify, black out, make dusky, deepen the shade, overshadow, make gloomy, screen, shut out the light, befog, keep out the light.

To become darker

grow dark, grow black, become dark, grow dim, blacken, turn to twilight, deepen into night, become gloomy, be overcast, grow dusky, cloud up, cloud over, overcloud, grow shadowy.

*To win by a narrow margin

barely win, win by a hairbreadth, nose out*; see defeat.