Tom Watts: Some liveries more exciting than others so far. Loving the @HaasF1Team black and gold and quite like the added blue on the @RacingPointF1 but disappointed by @redbullracing - same old same old.

Ben Shepherd: The weird thing is that I always obsess over testing, but then lose interest in the season itself. I think it might be because testing happens when I’m at my desk at work...

I hope your boss isn't looking at the BBC Sport website right now Ben?

If you didn't already know, Williams aren't here today, because their car isn't ready yet.

Deputy team principal Claire Williams says the car will run on Tuesday - the second of four days of testing at Barcelona's Circuit de Catalunya.

Last week, the British team cancelled a planned shakedown run of the car because of delays in building it.

"It's clearly not ideal, but equally it's not the end of the world," Williams said.

"Our absolute priority is to always ensure we bring a car to the track that is the best that it can be and sometimes that takes longer than you'd anticipate or like."

Read more here.

Image source, PA

But whose is better? Max or Pierre's?

Image source, Red Bull

Max Verstappen has got a sweet new lid for this season.

Image source, Red Bull

1. Vettel 1:19.137
2. Perez 1:20.652
3. Raikkonen 1:20.945
4. Sainz 1:21.230
5. Grosjean 1:21.500
6. Hulkenberg 1:21.633
7. Verstappen 1:21:808
8. Bottas 1:22.500
9. Kvyat 1:22.985

Euan: Someone needs to tell Vettel to stop listening to Dead or Alive.

Matt Richardson:Haven’t been this excited for a new F1 season in a long time. Hopefully testing will show relative competitiveness between the new cars.

Daniel: The Alfa testing livery was fantastic! Why did they change it?

Kayleigh: Soooo. I don’t like the McLaren livery, so it’s going to be a fun season for me! In love with the Renault wishing Red Bull would keep their testing livery all season, because that is something else!

It's a green flag and we're back on track, but Haas do actually need Green Flag.

Chris Medland
F1 journalist in Barcelona

It's the Ferrari-powered teams causing the red flags so far, as Romain Grosjean stops on track in the final sector.

Kimi Raikkonen had a spin in the Alfa Romeo earlier, this looks like a technical reason leading to a precautionary stop, with Grosjean pulling to the inside of the circuit just before the chicane. He's not far from the pit entry there, and it's downhill - but he jumped out of the car and has left it to the recovery truck to return it to the garage.

Haas tell me a loss of fuel pressure caused Grosjean’s stoppage. The team are investigating further back in the garage.

Image source, Getty Images

He just stopped after the final chicane, in his new VF-19 Haas. So it's back to the garage for Grosjean.

Chris Medland
F1 journalist in Barcelona

This is the first official start running of the season, but a number of teams have already completed shakedowns with their 2019 cars.

Haas have been here since Friday when they carried out a filming day in Barcelona, but the VF-19 is being seen in public for the first time today.

The team launched their livery in London 10 days ago, but that was on last year's car rather than the new design.

Romain Grosjean is behind the wheel for the opening day of the test, with Kevin Magnussen carrying out a number of media duties this morning - something drivers love even more than testing...

Image source, Getty Images

Ian McCormack: Alfa Romeo on the back of a recovery truck - the crossover between F1 and road cars is complete!

Phillip V: Gutted that the camouflage liveries of Red Bull and Alfa weren't kept on. Why must they tease us!

Antony Wilding: Lost - Williams F1 Car. Mainly white with flashes of blue and black on it's sides. Doesn't like tarmac. Please check all sheds and garages as it may be frightened and have taken refuge somewhere. Last seen in Oxfordshire.

Pierre Gasly has an update.

Vettel is currently top of the board with a 1:20.920 followed by:

2. Raikkonen 1:20.945

3. Perez 1:21.850

4. Sainz 1:22.348

5. Hulkenberg 1:23.665

6. Bottas 1:24.381

Chris Medland says: "He was on an out lap and stopped pointing at the pit entry. He quickly got out of the way and rejoined in the middle of the chicane and started his run as if nothing had happened."

Meanwhile Red Bull have stuck with their usual colours.

There are nine teams to officially unveil their car today.

Haas have already done earlier this morning.

We saw their black and gold livery last week on their 2018 car. But today is the real thing.

Image source, Getty Images

Andrew Benson
BBC Sport’s chief F1 writer

Racing Point this morning became the last team to unveil their 2019 car. The so-called RP19 (imaginative) bears a strong resemblance to last year’s Force India, particularly at the front, but technical director Andrew Green says this is very much a basic-spec car aimed at enabling the team to have a solid start to testing.

Developments are on their way for the first race of the season in Australia, over the first four races and, particularly, for the Spanish Grand Prix in early May, he says.

Image source, Getty Images

We will have updates for you across the eight days of testing from me (obviously), our chief writer Andrew Benson, and Chris Medland, an F1 journalist who is out in the paddock.