General Mills is dropping artificial colors and flavors from its cereals, the latest company to respond to a growing desire for food made with ingredients people see as natural. The company said on Monday that Trix and Reese’s Puffs will be among the first cereals to undergo the changes. As a result, the reformulated Trix cereal later this year will be made with four colors instead of six, said Kate Gallager, cereal developer for General Mills. While the company was able to come up with alternatives for red, orange, yellow and purple Trix pieces, Ms. Gallager said it was too difficult to find natural alternatives for blue and green that achieved the right taste and color. “We haven’t been able to get that same vibrant color,” she said. The Minneapolis company says cereals like Lucky Charms that have marshmallows may take longer to reformulate. The company said 90 percent of its cereals will have no artificial ingredients by the end of 2016. A range of food companies including Subway, Pizza Hut, Panera, Hershey and Nestlé have said in recent months that they are removing artificial ingredients from some or all products. General Mills, which also makes Cheerios and Cinnamon Toast Crunch, says more than 60 percent of its cereals are already made without artificial colors and flavors.