Gelatinnoth Mother

The Gelatinnoth Mother is a monster encountered during the final battles in the Recipe for Disaster quest. She is the equivalent to the Dagannoth Mother from the Horror from the Deep quest. She will turn different colours every 15 to 20 seconds, and her colour shows her weakness to a certain type of magic spell or attack.

The following table shows her colours in the order she cycles through them in the Defeating the Culinaromancer subquest and lists which attacks she is weak against in each state.

Players are faced with a dilemma on this monster, as they must defend against both melee and ranged attacks without using prayer, but be able to attack most of the time using magic. The challenge is to find a mix of armour that provides sufficient defence without imposing undue attack penalties.

A good set of armour is Full Ahrims with an Air staff and an Obsidian Shield, as this gives players a respectable mage attack bonus (which players need two-thirds of the time) and also allows players to have a balanced defence against the mother's attacks. Using high class melee armour such as Barrows even while using spells at 65+ Magic still works perfectly fine, as long as players use attacks to which the Mother is currently weak and which negate virtually all of her ranged damage throughout the encounter. (Players should still bring some high-healing food, however, for her melee.) Tested success rate with spells using this armour at Level 68 Magic was roughly 80% when using the appropriate elemental spell.

Another great way to get through this fight is with Void Knight equipment. You can cycle through powerful melee, magic, and ranged armour by exchanging the helms. The armour also gives a good defence against all types of attacks.

A slightly less exotic armour mix that works is a mage top and bottom (such as Skeletal armour, Splitbark armour, or Lunar equipment), a Helm of neitiznot or Dragon med helm, and a Rune kiteshield. This combination still has a significant ranged attack penalty, but players can wait until the Mother switches vulnerabilities to begin attacking again or use a Dwarf multicannon, since those are allowed at the battle site.

This is the official spoiler from the runescape quest help page

The key to the Gelatinnoth Mother fight is in knowing what attack to use, and when to use it. Luckily I remember a rhyme I heard a long time ago.
Orange is the metal which cools to form a blade, Green are the trees from which arrows are made, Red is fire which blazes hot and true, and brown is the earth beneath me and you.

Blue are the waters of rivers and streams, and white for the winds which carry our dreams!

I finally understand the words. The blade represents melee combat which I should use when the beast is orange.

I will be best off ranging it when it turns green, and using fire spells when it turns red.

When it becomes brown I should switch to earth spells, and blue means I will need to use water spells.

Finally when it turns white I can assault it with air spells. I have also noticed she always follows the same sequence of colours. She starts white, then turns blue, followed by orange, brown, red and finally green. Predictability! Yet another chink in her armour.

Now I know the weakness of the Gelatinnoth I can attack it for massive damage, but I'll still need to keep a careful eye on my own health and have plenty of food with me.

The Gelatinnoth Mother uses a Ranged attack to hurt me, so I should wear a set of armour with really good ranged defence. Rune and dragon armours have very good all round defence and will certainly be good enough for this fight, but if I want to be almost impervious to the Gelatinnoth Mother's attacks I might consider investing in a set of granite armour.