It could possibly be a defective lamp. It sounds that the lamp is mercury starved. All phosphored mercury lamps starts with a more or less pink glow. That glow goes away as the pressure of the lamp rises. If there's not enough mercury, the pressure stays low.
To be more exact, a low pressure mercury discharge emits very little visible light, but a lot of UV light. The UV excites the phosphor, giving the pink glow, but because almost no visible light is generated (due to the abnormally low pressure), the spectrum isn't balanced by the blue light normally emitted by a higher pressure mercury discharge.
Hope this helps