The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example to understand incomplete dominance. In a cross between truebreeding red-flowered (RR) and true-breeding white- flowered plants , the was pink.
When the was self-pollinated the it resulted in the following ratio 1 (RR) Red: 2 (Rr) Pink: 1 (r) White. Here the genotype ratios were exactly as we would expect in any mendelian monohybrid cross, but the phenotype ratios had changed from the dominant: recessive ratio.
What happened was that R was not completely dominant over r and this made it possible to distinguish as pink from RR (red) and rr (white).