On heating glucose with Fehling solution, we get a precipitate whose colour is 
 

Fehling's solution contains copper(II) ions complexed with tartrate ions in sodium hydroxide solution. Complexing the copper(II) ions with tartrate ions prevents precipitation of copper(II) hydroxide

The reducing group of glucose (-CHO) is oxidized by the Cu²⁺ ions in Fehling's to Cu⁺ (red copper oxide). 

${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+2\mathrm{CuO}⟶{\mathrm{C}}_5{\mathrm{H}}_{11}{\mathrm{O}}_5.\mathrm{COOH}+\underset{\mathrm{Red} \mathrm{precipitate}}{{\mathrm{Cu}}_2\mathrm{O}}\downarrow$