The joint-headline show will be the first time the two bands have performed with each other since they toured together back in the 80s.
"It's our first time on the same bill since the end of the Brave New World tour in 1983," says Trilogy bassist Mark Bloxsidge. Both bands also featured on the 1985 prog compilation album Fire In Harmony.
Essex trio Trilogy reunited in 2021 to record new online video for their song Break! and also conformed earlier this year that they would be looking to be playing live to celebrate the band's 40th anniversary.
Solstice have been active for a lot longer and are currently riding a wave of creativity and success with the arrival of new vocalist Jess Holland and the release of 2020's Sia album. They will release their latest album, Light Up, through GEP early next year.
Tickets for the Colchester show are priced at £15. Doos open at 7.30pm, with the show starting at 8pm.