Ray of Frost — ruling 1

If the enchanted creature is red (or if it becomes red), it loses all abilities that it had prior to the time Ray of Frost became attached to it. It will keep any abilities that were granted to it after Ray of Frost became attached to it.

Ray of Frost — ruling 2

If the enchanted creature is red and has a characteristic-defining ability that specifies its types or colors, that ability will still have its effect because it's applied before the creature loses the ability.

Ray of Frost — ruling 3

If the enchanted creature is red and has a characteristic-defining ability that specifies its power and/or toughness, that ability will not have its effect. In that case, its power and/or toughness (as appropriate) become 0.

Ray of Frost — ruling 4

Some noncreature permanents, such as Grand Master of Flowers, become creatures because of a static ability they have. If Ray of Frost becomes attached to such a creature and that creature is red or becomes red, that permanent will remain a creature even though it loses the ability that is making it a creature after that ability applies.

Ray of Frost : règles, fonctionnement et interactions (MTG)

Ray of Frost is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flash Enchant creature When this Aura enters, if enchanted creature is red, tap it. As long as enchanted creature is red, it loses all abilities. Enchanted creature doesn't untap during its controller's untap step.

How it works : Ray of Frost

Original English text — Wizards of the Coast / Scryfall

#1July 23, 2021· Wizards of the Coast
If the enchanted creature is red (or if it becomes red), it loses all abilities that it had prior to the time Ray of Frost became attached to it. It will keep any abilities that were granted to it after Ray of Frost became attached to it.
No other card is named in this ruling.
#2July 23, 2021· Wizards of the Coast
If the enchanted creature is red and has a characteristic-defining ability that specifies its types or colors, that ability will still have its effect because it's applied before the creature loses the ability.
No other card is named in this ruling.
#3July 23, 2021· Wizards of the Coast
If the enchanted creature is red and has a characteristic-defining ability that specifies its power and/or toughness, that ability will not have its effect. In that case, its power and/or toughness (as appropriate) become 0.
No other card is named in this ruling.
#4July 23, 2021· Wizards of the Coast
Some noncreature permanents, such as Grand Master of Flowers, become creatures because of a static ability they have. If Ray of Frost becomes attached to such a creature and that creature is red or becomes red, that permanent will remain a creature even though it loses the ability that is making it a creature after that ability applies.
No other card is named in this ruling.