Leaving the conditioner in my hair didn't change my hair color. If it looks different from older photos, most of that is just different lighting/exposures on the camera.

My hair is naturally dark brown/black, so in shadows it looks black, but in the sun it looks reddish brown. Also, as anyone's hair gets longer, the ends tend to get lighter because after 8 years or so (the time it takes for them to get past the waist), the ends have seen a lot of sun, which is what makes them look lighter.

I did put in a few highlights a few years ago, so I have some streaks of lighter brown in my hair, but I'm growing them out now.

So leaving in a conditioner that's good for your hair won't change your color in the slightest. Sun exposure will slowly lighten your ends over time.

The only way to protect your ends from getting lighter is to keep your hair in a bun or under a hat when you were in the sun. And no matter what a hair protection product says—to be totally safe—it's best to protect your hair from being directly in the sun. Also, no matter what a sun-protecting hair product may say on the bottle, if they don't have an SPF rating printed on them, you have no idea if they'd work (or how well they'd work) to protect your hair from the sun. Saying a product can protect your hair from sun damage is more marketing hype than anything (they don't have to tell you the truth on their packaging), and the only safe thing is to shield your hair (just like your skin) from being directly out in the sun.