Materialgirl (and now I'll have that song stuck in my head all day...LOL), first welcome to the forum.
Second TomatoSoup (TS) is right. The dead give away as to what you have is the 2.4L engine. Your car though does have one option. The red/black interior was not standard on the Sky but was available to all models. Also, there really are only two models to the Sky, the base 2.4L and the Turbocharged 2.0L Redline model. Other than the engine, there are some other minor visual cues.
From the front, there are two very distinctive differences:
The first is headlight color. The base models have chrome headlights while the Redlines all received black headlights. Now the headlights are interchangeable and some 2.4 owners have installed the Redline style headlights. Note however that in Europe our Sky was sold as the Opel GT. That car was basically a Redline but for the Opel, GM used the chrome headlights rather than the black.
The Opel GT and the Redline however both share the other difference that you see up front. If you look at the lower grill you'll notice the vents by the turn signals / fog lights looks different on both cars. The 2.4 has a chrome strip across it and the Redline does not. That is the visual difference. The functional difference is that on the Redline those vents work to direct air towards the front brakes.
From the side, there is only one subtle difference between the two cars.
Here the only difference is in the side vent. If you look at the picture of the Redline, you'll note there is a little strip of silver. This is the vent insert. On all Redline models, this insert was silver. On the 2.4 models, it was the same color as the car.
The rear is much like the front with two differences, one major, one minor:
The most obvious difference is in the exhaust. The 2.4 model has a single exhaust on the passenger side while the Redline has a dual exhaust. The Redline exhaust will fit on a 2.4 so long as you either 1) get a Redline rear valance that has the second cutout for the second tip or 2) cut out the section of the stock 2.4 valance for the second tip. On both my 2.4s I have done the latter and you cannot tell it was cut out unless you know what you're looking for and look REAL close.
The second, less obvious, difference is in the badging. The 2.4 just has the word SKY on the driver's side rear bumper. The Redline has the same style badge in that location but next to the word SKY is a small silver box with a horizontal red line through it (see what they did there...red line...Redline...those quirky GM engineers...). The other difference is there is a silver TURBO badge on the passenger's side of the rear bumper. It should be noted though that these badges can be removed and replaced with the other model's badges though I'm not sure of ANYONE who has done that. Usually if people touch these badges they remove them completely.
That's all the visual cues you get between the cars. Everything else is the same. Now mechanically, other than the turbocharged engine, the Redline also got firmer suspension in the form of different shocks/springs and thicker front and rear anti-sway bars. Once again that can all be upgraded on either car however.
So welcome again to the forum and I hope this helps you identify fellow Sky owners. Our Pontiac Solstice cousins (same car, different body work) have the same two types of models but they have the 2.4 base and a 2.0 Turbo badged as the GXP. Their visual differences are a bit more subtle than ours other than in the rear (GXP and turbo badge plus dual versus single exhaust outlets).
And now I'm off to bop around the office humming Madonna.