How do I set a pin of 8051 high?

I'm using Keil to program the AT89C52 Microcontroller. I define a sbit to be a single pin of a port.

For eg: sbit a = P0 ^ 0;

But when I set a = 1, then I get the pin in a gray color in proteus where I run the program on simulated hardware. For high, the pin should be red. I'm trying to interface the LM041L LCD. Please help. I'm very new to this and I don't understand what is casing this

The 8 pins on P0 are in open drain mode by default. When you use these 8 pins as outputs, you should imply a pull up resistor in order to output a high signal.