The Disneyland Resort has announced dates and details for its 2018 'Merriest Place on Earth' event:

Quote Originally Posted by Disney Parks & Resorts

Holidays at the Disneyland Resort will return once again this year, bringing seasonal magic to the Merriest Place on Earth November 9 through January 6. This festive season will include the return of favorite holiday experiences and entertainment, as well as dazzling decor decked out throughout the resort!

At Disney California Adventure park, Festival of Holidays will again bring the spirit of the season to life through special entertainment, including the return of Disney ¡Viva Navidad! street party. Delicious food at the guest-favorite Festive Foods Marketplace will present a mix of holiday dishes and beverages that bridge many diverse cultures and family traditions. For the residents of Cars Land, two attractions will receive their holiday overlay again this year to become Luigi’s Joy to the Whirl and Mater’s Jingle Jamboree.

At Disneyland park, seasonal fan favorites return, including the enchanting Sleeping Beauty’s Winter Castle, “Believe … in Holiday Magic” fireworks spectacular and magical “A Christmas Fantasy” parade. In addition, seasonal transformations will once again take over “it’s a small world” Holiday and Haunted Mansion Holiday.
Although seperate dates & details could be announced later, it appears that a seasonal edition of World of Color is not currently planned as part of the 2018 event. The current refurbishment is listed as through "Late 2018".