Setting particle emitter color range makes particles black

## Environment
* OS Version:
* Source or binary build? source, garden

## Description
* Expected behavior: Setting color range for particles affect particle color
* Actual behavior: Particles always appear black

The [Ogre2ParticleEmitter::SetColorRange](https://github.com/gazebosim/gz-rendering/blob/6fa1fc184d052b5235fa7ad7b75c9682142df39f/ogre2/src/Ogre2ParticleEmitter.cc#L295) function is working fine in the `ign-rendering6` branch which is on ogre2.2. The `gz-rendering7` branch is on ogre2.3. Looking at the ogre-next code base, I don't see many changes in the particle system between `v2-2` and `v2-3` branches. There haven't been any related changes in the [Ogre2ParticleEmitter.cc](https://github.com/gazebosim/gz-rendering/blob/gz-rendering7/ogre2/src/Ogre2ParticleEmitter.cc) as well. The bug might be coming from other parts of gz-rendering when we upgraded from ogre 2.2 to 2.3.

## Steps to reproduce
Modify the particle_demo and change [the line](https://github.com/gazebosim/gz-rendering/blob/6fa1fc184d052b5235fa7ad7b75c9682142df39f/examples/particles_demo/Main.cc#L132) from"

```cpp
areaEmitter->SetColorRangeImage(RESOURCE_PATH + "/smokecolors.png");
```

to

```cpp
areaEmitter->SetColorRange(math::Color(1, 0, 0), math::Color(0, 1, 0));
```

The particles flowing upward from below the duck appear black instead of turning color from red to green

## Output


Start with Ogre2ParticleEmitter::SetColorRange in ogre2/src/Ogre2ParticleEmitter.cc and the reproduction change in examples/particles_demo/Main.cc. Compare the working ign-rendering6 behavior with gz-rendering7 and the Ogre 2.2 versus 2.3 particle-system code. Done means the particle demo renders the configured color range from red to green instead of black.

Written by the indexing model from the issue text.