An experiment someone should do at some point (if it hasn't already been done):

Divide (educated Western) subjects into two groups. Ask the first group how much they think life has improved in a particular African country since decolonization, without mentioning the date of the latter. Ask the second group how much they think life in that country has improved since 1950 (or whatever the actual appropriate date for "decolonization" is for the country selected), without mentioning colonization. Compare the results.

Prediction: the second group's answer will be higher.