dihydroxyphenylcarboxy pentane as the electron accepting compound used in example 23 was replaced by the same parts of 1 3 bis 3 5 dihydroxyphenylcarboxy propane therein the remaining rate of the developed color density was found to be 98 the heat resistance evaluation of the color developed area was made in the same manner as in example 23 except that 1 5 bis 3 5 dihydroxyphenylcarboxy pentane as the electron accepting compound used in example 23 was replaced by the same parts of 1 4 bis 3 5 dihydroxyphenylcarboxy butane therein the remaining rate of the developed color density was found to be 87 the heat resistance evaluation of the color developed area was made in the same manner as in example 23 except that 1 5 bis 3 5 dihydroxyphenylcarboxy pentane as the electron accepting compound used in example 23 was replaced by the same parts of 1 6 bis 3 5 dihydroxyphenylcarboxy hexane therein the remaining rate of the developed color density was found to be 85 the heat resistance evaluation of the color developed area was made in the same manner as in example 23 except that 1 5 bis 3 5 dihydroxyphenylcarboxy pentane as the electron accepting compound used in example 23 was replaced by the same parts of 1 5 bis 3 5 dihydroxy 4 methylphenylcarboxy pentane therein the remaining rate of the developed color density was found to be 86 the heat resistance evaluation of the color developed area was made in the same manner as in example 23 except that.