Photoelectric Sensor for Eyemarks reading/ color reading

I have made an optical sensor using Photo diode and a white bright LED, the concept is like pep-rel sensors, LED is transmitting light on the eyemark and photo-diode is sensing light intensity that is returning from the object which is passing from front of the both of LED and Photo-diode. I am storing Average analog reading in EEPROM and comparing it from real time reading. The data of Cardboar color is almost very near, but the data of eyemark reading is very different from the one average saved into the EEPROM. Please suggest me.

Schematic is based on : Bright LED with 3.3 Volt and PhotoDiode is using Reverse Biased with 10K Resistor from Ground to VCC - Analog is reading from that point

SerialReadWrite.ino (1.64 KB)