Power dissipation of TLC6C5712-Q1 LED Driver IC
You are right in taking the reference voltage to calculate power dissipated. \$V^2/R\$    

Take the worst case voltage (1.254 V).   



Edit 2: How do i calculate power consumed by the driver:  

Supply current times the input voltage will give the power consumption of the device. 

  



Edit 3: Here are my observation: 


The TLC6C598 is a simple current sink. It can sink upto 50 mA (limited by rating of the transitors). The TLC6C5712 is a constant current driver  
The current limit in TLC6C598 set using external resistors (one per channel). The current limit in TLC6C5712 is set using single resistor (at IREF pin).  
TLC6C598 is for simple LED designs where as the TLC6C5712  is used for compensating LED  color temperature and brightness.     
PWM support is there in both 







Edit 3:  

The blue colored section, will be very tiny. you can ignore.